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Documents Folder Title Following special characters are not supported: \ / ? % * : | " < > Privacy Public All Members My Connections Only Me Cancel Create 000231.html 4 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] X215 comments re microphones </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] X215 comments re microphones</H1> <B>neil a shaw</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20X215%20comments%20re%20microphones&In-Reply-To=%3C5453A473.7050505%40ieee.org%3E" TITLE="[SC-04-08] X215 comments re microphones">menlo at ieee.org </A><BR> <I>Fri Oct 31 09:02:11 MDT 2014</I> <P><UL> <LI>Previous message: <A HREF="000230.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000232.html">[SC-04-08] X215 comments re microphones </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#231">[ date ]</a> <a href="thread.html#231">[ thread ]</a> <a href="subject.html#231">[ subject ]</a> <a href="author.html#231">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>All- This question was discussed within the B-chain SG. Where to aim for the screen channels - left, center, or right? Where to aim for the surround channels? That is why straight up was chosen - the microphones are in the same orientation for all loudspeakers located for 7.1 and 5.1 systems (but maybe not for the ceiling loudspeakers in immersive systems - that is a bridge too far right now). Maybe not the most rigorous solution, but definitely a practical one. I welcome any comments as this is what Tom Holman called a nuisance variable, and needs to be addressed to insure conformance and repeatability. Thanks. Neil Neil A. Shaw, FASA, FAES Menlo Scientific Acoustics, Inc. Topanga, California +310-455-2221 On 10/31/14 2:21, John Woodgate wrote: ><i> In message <000d01cff4e8$f99b5390$ecd1fab0$@acousticdirections.com>, </I>><i> dated Fri, 31 Oct 2014, Glenn Leembruggen </I>><i> <<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">glenn at acousticdirections.com</A>> writes: </I>><i> </I>>><i> I believe it to be easier and less prone to error to use a free-field </I>>><i> microphone that is simply pointed at the loudspeakers. </I>><i> </I>><i> At some microphone positions, loudspeakers may be spread over </I>><i> directions approaching +/-75 degrees, if not more. Where do you point </I>><i> the microphone? </I> </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000230.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000232.html">[SC-04-08] X215 comments re microphones </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#231">[ date ]</a> <a href="thread.html#231">[ thread ]</a> <a href="subject.html#231">[ subject ]</a> <a href="author.html#231">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000232.html 3 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] X215 comments re microphones </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] X215 comments re microphones</H1> <B>John Woodgate</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20X215%20comments%20re%20microphones&In-Reply-To=%3CfOomO%2BuOn6UUFwIk%40jmwa.demon.co.uk%3E" TITLE="[SC-04-08] X215 comments re microphones">jmw at jmwa.demon.co.uk </A><BR> <I>Fri Oct 31 09:25:02 MDT 2014</I> <P><UL> <LI>Previous message: <A HREF="000231.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000233.html">[SC-04-08] X215 comments re microphones </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#232">[ date ]</a> <a href="thread.html#232">[ thread ]</a> <a href="subject.html#232">[ subject ]</a> <a href="author.html#232">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>In message <<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">5453A473.7050505 at ieee.org</A>>, dated Fri, 31 Oct 2014, neil a shaw <<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">menlo at ieee.org</A>> writes: ><i> That is why straight up was chosen - the microphones are in the same </I>><i>orientation for all loudspeakers located for 7.1 and 5.1 systems (but </I>><i>maybe not for the ceiling loudspeakers in immersive systems - that is a </I>><i>bridge too far right now). </I> Agreed. I suspect that immersive systems require a whole new protocol. ><i> Maybe not the most rigorous solution, but definitely a practical one. </I> From David Josephson's report, 'pointed at the ceiling' is preferred, and works for everything (except immersive), rather than being 'not the most rigorous'. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Quid faciamus nisi sit? John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000231.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000233.html">[SC-04-08] X215 comments re microphones </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#232">[ date ]</a> <a href="thread.html#232">[ thread ]</a> <a href="subject.html#232">[ subject ]</a> <a href="author.html#232">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000233.html 5 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] X215 comments re microphones </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] X215 comments re microphones</H1> <B>David Josephson</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20X215%20comments%20re%20microphones&In-Reply-To=%3C5453C6D1.7030603%40josephson.com%3E" TITLE="[SC-04-08] X215 comments re microphones">dlj at josephson.com </A><BR> <I>Fri Oct 31 11:28:49 MDT 2014</I> <P><UL> <LI>Previous message: <A HREF="000232.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000235.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#233">[ date ]</a> <a href="thread.html#233">[ thread ]</a> <a href="subject.html#233">[ subject ]</a> <a href="author.html#233">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>On 10/31/14 8:02 AM, neil a shaw wrote: ><i> This question was discussed within the B-chain SG. Where to aim for the </I>><i> screen channels - left, center, or right? Where to aim for the surround </I>><i> channels? That is why straight up was chosen - the microphones are in </I>><i> the same orientation for all loudspeakers located for 7.1 and 5.1 </I>><i> systems (but maybe not for the ceiling loudspeakers in immersive systems </I>><i> - that is a bridge too far right now). Maybe not the most rigorous </I>><i> solution, but definitely a practical one. </I>><i> </I>><i> I welcome any comments as this is what Tom Holman called a nuisance </I>><i> variable, and needs to be addressed to insure conformance and </I>><i> repeatability. </I> Can anyone say why the "straight up" method would be any less rigorous than any other method described here? Few users in this community are willing to spend the time and/or money to calibrate their microphones by free-field reciprocity. Without that, you're at the mercy of whatever correction curve the manufacturer supplies, whether it's pressure coupler to normal incidence response, or electrostatic actuator to normal incidence. The general trend of the curve is well established by the physics of scattering, but details in the top octave, and at different angles, are determined by specifics of the protection grid and housing of the microphone. Nearly all microphones incorporate internal damping and equalization whenever the wavelength of sound is shorter than the significant dimensions of the microphone. It doesn't matter for our purposes whether this equalization is mechanical, as in the case of differentiating legacy pressure-response, random-incidence, diffuse- or free-field microphones, or electrical. It is no less rigorous to apply external equalization to achieve the calibrated response, than to accept the manufacturer's assertion that their mechanical equalization is accurate. The last part of my comment included specific recommendations for a series of specifications that could be used to establish the utility of a given microphone for this application. The degree of rigor is set by the user's requirements for precision and traceability of each measurement, and we should all know how to add up the error bars to determine how close we are to "exact." David Josephson </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000232.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000235.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#233">[ date ]</a> <a href="thread.html#233">[ thread ]</a> <a href="subject.html#233">[ subject ]</a> <a href="author.html#233">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000234.html 11 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration"; mark yonge </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"; mark yonge</H1> <B>Glenn Leembruggen</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22%3B%20mark%20yonge&In-Reply-To=%3C02fa01cff572%241d688660%2458399320%24%40acousticdirections.com%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"; mark yonge">glenn at acousticdirections.com </A><BR> <I>Fri Oct 31 19:21:06 MDT 2014</I> <P><UL> <LI>Previous message: <A HREF="000227.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration"; mark yonge </A></li> <LI>Next message: <A HREF="000226.html">[SC-04-08] Comments on X215 </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#234">[ date ]</a> <a href="thread.html#234">[ thread ]</a> <a href="subject.html#234">[ subject ]</a> <a href="author.html#234">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>Mark Where do I send or post my marked up Word document for Modern Cal. I sent by email last night but it bounced due to attachment size. thanks Glenn Glenn Leembruggen Acoustic Directions Pty Ltd Consultants in Acoustics & Sound Systems tel: +612 9568 4684 fax: +612 9572 8939 mob: +61 418 207 085 -----Original Message----- From: <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A> [mailto:<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A>] On Behalf Of Glenn Leembruggen Sent: Friday, 31 October 2014 7:37 PM To: 'Working group on Measurement and equalization of sound systems in rooms' Subject: Re: [SC-04-08] Comments on "SMPTE-Modern-Calibration"; mark yonge Hello Mark Re your comment regarding the USE OF ST 202 WITH FFT-BASED ANALYSER and following sections, I'm not sure if I have misunderstood you. The work that was presented in the B Chain report showed beyond doubt that the mechanism producing the X curve had nothing to do with the reverberant buildup in the room. The X curve results from the low pass filter action of the perforated screens, a small amount of air loss and whatever the drivers are doing. Cheers Glenn Glenn Leembruggen Acoustic Directions Pty Ltd 14 65-67 Crystal St Petersham 2049 Australia PO Box 205 Summer Hill 2130 tel: +61 2 9568 4684 fax: +61 2 9572 8939 mob: +61 418 207 085 The information contained in this e-document and any file attachments is confidential to all parties except the intended recipients. If you are not an intended recipient you have received this document in error and are prohibited from disclosing or using any of the information contained. We would be grateful if you would advise us of such errors immediately by return email. Thank you. -----Original Message----- From: <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A> [mailto:<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A>] On Behalf Of Mark Yonge Sent: Monday, 27 October 2014 6:31 PM To: <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08 at standards.aes.org</A> Cc: Mark Yonge Subject: [SC-04-08] Comments on "SMPTE-Modern-Calibration"; mark yonge INTRODUCTION These comments relate to SMPTE's draft RP document on Modern-Calibration: original filename: "SMPTE-Modern-Calibration-RP-for-AES-comment 2014-10-02.docx" Posted 2014-10-03 to SC-04-08 as "x215-141002-DRAFT-SMPTE-Modern-Calibration.docx" COMMENTS GENERAL RP This "recommended practice" appears to leave much is left to the discretion and experience - "knowledgeable interpretation" - of the technician. Becaus individual cinemas can vary greatly, this is understandable and, I believe necessary. However, this argues against using unskilled technicians in this role, which may have been one of the intended goals. INSTALLATION VS CHECKS Prefer to keep installation issues separate from subsequent checks. It should be possible to confirm the satisfactory alignment of the system without changing any calibration. A simplified procedure for go/no-go performance checks could be included as an annex, with references to the main installation text where necessary. EFFICIENCY How much time should this process take? Would it be better to structure the document for smoother flow on the night? Keep movements between the projection booth, auditorium, and the behind-screen area to a minimum. USE OF ST 202 WITH FFT-BASED ANALYSER The X-curve in ST 202 depends entirely on measuring the acoustic reproduction of continuous pink noise in a reverberant auditorium using a traditonal 1/3-octave real-time audio analyser (TRA). The deviation of the X-curve from a flat trace results from the reverberation contribution which has a higher spl than the direct sound and is dominant at lower frequencies. ST 202 does not specify or require any filter in the signal path; its intent is to allow an imperfect measurement tool (RTA) to predict the amplitude and spectrum of the reverberation component to deduce spectrally-flat direct sound arriving at a typical seat in the auditorium. Unless the FFT analyser in this RP emulates the behaviour of an RTA precisely, the X-curve in ST 202 becomes irrelevant, and a new characteristic needs to be found. (see also below) CLAUSE-SPECIFIC COMMENTS NORMATIVE REFS IEC 61260 Ed.1:1995 has been superseded by IEC 61260-1 Ed.1:2014 " Electroacoustics - Octave-band and fractional-octave-band filters - Part 1: Specifications". I believe that the specifications in the international standard are equivalent to those in ANSI/ASA S1.11. Is it useful to cite both as normative references? TERMINOLOGY Decibel The unit "decibel" is spelled without a mid-cap. The bel, used alone, does not have a capital letter, according to SI. Sampling rate vs sampling frequency Just FYI, it is AES practice to refer to "sampling frequency" (in units of Hertz: Hz) where the sample-timing must be regular - such as in conversion, quantization and re-quantization - and "sampling rate" (in units of kilosamples per second: ksps) where the timing is more loosely-defined, such as in packetized streams, for example. 8.1 LOUDSPEAKERS The draft states, " Verify that all surround loudspeakers with a built-in switchable X-Curve filter are set to the same switch position. It is recommended that such switches be set to flat or off." This implies that some loudspeakers in cinemas have "X-curve" filters fitted. This is fundamentally to misunderstand the X-curve (see above). I can see no purpose for any generalized filter in the signal path of a loudspeaker. I understand that an RP must use the language of recommendation, but propose to replace "recommended" with "strongly recommended" at least. Same comment at A.18.5.2.2 16 DISTORTION SWEEP The proposed single-tone sweep from 20 Hz to 16 kHz seems unnecessarily wide for this purpose. Distortion harmonics of signals above about 8 kHz will be outside the audible spectrum, and the very high level proposed for this sweep (-3 dB FS) will risk damaging components at these high frequencies. Suggest restricting the single-tone high-level sweep to 20 Hz to 8 kHz, max. 18.5.1 SCREEN CHANNEL ELECTROACOUSTIC MEASUREMENTS The type of analysis to be used for these frequency response measurements is not well defined in this clause, and it's very important that it is. 18.5.1 describes using the analyser in transfer-function mode. But 18.5.1.1 asks for adjustments to fit the ST 202 X-curve. Unless I have misunderstood the meaning of "transfer-function mode", and the analyser actually does emulate precisely a traditional RTA measurement, this just doesn't work! To summarize, both cases assuming a continuous pink-noise stimulus: • A single-channel measurement that has been arranged to emulate precisely a traditional RTA measurement, and which measures the whole signal from the microphone including the reverberation component, should be used with the ST 202 X-curve. • A dual channel measurement that uses the source signal to discount the reverberation component in the received microphone signal should NOT be adjusted to the X-curve: it should probably be calibrated to a flat response. Either measurement technique should give an equivalent electroacoustic response in the auditorium - flat direct sound. Same comment at A.18.1 Clarity here is vital, I think. Mark Yonge vice chair, SC-04-08 <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">mark.yonge at aes.org</A> _______________________________________________ SC-04-08 mailing list <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">SC-04-08 at standards.aes.org</A> <<A HREF="http://standards.aes.org/sc.cfm?ID=91">http://... Expand This file was truncated for preview. Please download to view the full file. 000235.html 6 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration" </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"</H1> <B>markyonge</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22&In-Reply-To=%3C746BC9B5-8886-496C-B9D7-B24D38E5E43E%40aes.org%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"">mark.yonge at aes.org </A><BR> <I>Tue Nov 4 07:31:38 MST 2014</I> <P><UL> <LI>Previous message: <A HREF="000233.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000236.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#235">[ date ]</a> <a href="thread.html#235">[ thread ]</a> <a href="subject.html#235">[ subject ]</a> <a href="author.html#235">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>Dear SC-04-08, This discussion of the SMPTE ST 202 X-curve, developed in the late 1970s, would only be of arcane historical interest, except for the suggestion that it might be perpetuated in the Modern Calibration draft using a different measurement technique. In the late 1970s I aligned many cinemas for Dolby Laboratories, who were active in developing the X-curve as a pragmatic tool to calibrate the B-chains of mix rooms and cinemas. The intent was to take full advantage of the essentially-flat A-chain frequency response in Dolby Stereo films. The measurement equipment that was available seemed like rocket science at the time, but now looks very dated. The measurement technique produced reasonably consistent results, but relied heavily on some working assumptions, many of which are also now outdated. The following assertions are fully supported by SMPTE ST 202:2010 (and its close cousin, ISO 2969). I am happy to go into this in more detail, developing the presentation I gave to SC-04-08 in Rome, May 2013. Meanwhile: • The purpose of the X-curve is to predict a flat frequency response for direct (first-arrival) sound; • The X-curve is a measurement artifact and not an audio roll-off; • The X-curve represents a display on a real-time audio analyser (RTA), comprising a flat spectral component of the direct sound overlaid at lower frequencies by a higher-amplitude reverberation contribution from the cinema auditorium. (The direct sound comprises instantaneous energy at the microphone, while the reverberant energy has been integrating for perhaps as long as a second in a "typical" cinema, building up to a higher amplitude). The X-curve is directly useful ONLY under the following circumstances: • A "typical" cinema - in the 1970s this meant between approximately 200 and 2000 seats with the typical reverberation characteristics of a vaudeville theatre; • Continuous pink noise - other stimuli exist that will not produce the same reverberation component and will not produce a satisfactory X-curve display; • 1/3-octave real-time audio analyser (RTA). The X-curve is NOT useful under the following circumstances: • Small cinemas, screening rooms, preview theatres, music studio control rooms, home theatres; • Very large cinemas; • Open-air cinemas, sports stadia; • Any cinema acoustically treated to reduce its reverberation; • Discontinuous test signals; • Any spectrum-analysis tool that isn't a 1/3-octave RTA. In such circumstances where the X-curve is not useful, the X-curve should be ignored and the best available measurement technique should be used to produce a flat frequency response for direct (first-arrival) sound arriving at a typical audience position. Let me be clear: An auditorium equalised to the X-curve inappropriately is very likely to lack high-frequency energy and will sound dull. I do not believe that references to the X-curve should be continued in this Modern Calibration draft now that the measurement tools and cinema acoustics have changed sufficiently to take its application out of the main stream - it is, in effect, obsolete. Correspondence on this reflector has invoked various alternative explanations for the X-curve, referring to external papers unavailable to this group. If these papers contain some engineering wisdom relevant for this discussion, then it would be appropriate to post those papers to this group AND to identify the relevant text with reference to the corresponding clause numbers in ST 202. A bit of rigour would be appropriate - as engineers, we have a duty to keep science and folklore separate. Sincerely, Mark Yonge vice chair, SC-04-08 </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000233.html">[SC-04-08] X215 comments re microphones </A></li> <LI>Next message: <A HREF="000236.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#235">[ date ]</a> <a href="thread.html#235">[ thread ]</a> <a href="subject.html#235">[ subject ]</a> <a href="author.html#235">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000236.html 4 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration" </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"</H1> <B>John Woodgate</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22&In-Reply-To=%3CGS5gZiJAJPWUFwK2%40jmwa.demon.co.uk%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"">jmw at jmwa.demon.co.uk </A><BR> <I>Tue Nov 4 08:35:28 MST 2014</I> <P><UL> <LI>Previous message: <A HREF="000235.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000237.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#236">[ date ]</a> <a href="thread.html#236">[ thread ]</a> <a href="subject.html#236">[ subject ]</a> <a href="author.html#236">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>In message <<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">746BC9B5-8886-496C-B9D7-B24D38E5E43E at aes.org</A>>, dated Tue, 4 Nov 2014, markyonge <<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">mark.yonge at aes.org</A>> writes: ><i> </I>A bit of rigour would be appropriate - as engineers, we have a duty to ><i>keep science and folklore separate. </I> The whole message is a valuable clarification. Let us rename the concept as the EX-curve. (;-) However, it is often very difficult to separate science and folklore, because people forget, or are too young to remember. 'Negative feedback reduces THD numerically but can actually make distortion musically worse.' Even back in 1978, Peter Baxandall ('Wireless World') implied that that statement was becoming treated as folklore, but it was true then and it's true now. This is OT for SC-04-08, but if you want to make an excellent amplifier using feedback, you must make the forward path as linear as you can possibly make it. (There's a thing about push-pull matched FETs that bears further investigation in that context, but that's for later.) -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Quid faciamus nisi sit? John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000235.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000237.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#236">[ date ]</a> <a href="thread.html#236">[ thread ]</a> <a href="subject.html#236">[ subject ]</a> <a href="author.html#236">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000237.html 4 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration" </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"</H1> <B>David Josephson</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22&In-Reply-To=%3C5458F54A.5010309%40josephson.com%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"">dlj at josephson.com </A><BR> <I>Tue Nov 4 08:48:26 MST 2014</I> <P><UL> <LI>Previous message: <A HREF="000236.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000238.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#237">[ date ]</a> <a href="thread.html#237">[ thread ]</a> <a href="subject.html#237">[ subject ]</a> <a href="author.html#237">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>Mark, thank you for that summary of the key issue here. I think many might have missed that it *is* really that simple, from a measurement point of view. Measuring with pink noise and an RTA includes the reverberant contribution of the room, measuring the transfer function from a speaker does not. Using a random-incidence/diffuse-field/pressure response microphone oriented vertically is appropriate when you want to capture the reverberant energy from the room, i. e. when using pink noise and an RTA. Using a free-field microphone pointed at the speaker being measured is appropriate only when you want to measure the direct response from that speaker, using transfer function or system identification analysis. That's useful for determining whether a given speaker is functioning normally, but does not *by itself* predict what the listener would experience. I suggest that the current effort be considered only a stepping stone to a future measurement method. I believe -- people more involved in the artistic decisions should decide this -- that the intent is to measure the listener experience, not the individual speaker contribution to it. If that's so, we need to use more intelligent metrics, based on transfer function measurement but including the room reverberant response. That is certainly doable but not with the methods suggested so far. David Josephson Chair, SC-04 Subcommittee on Acoustics </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000236.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000238.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#237">[ date ]</a> <a href="thread.html#237">[ thread ]</a> <a href="subject.html#237">[ subject ]</a> <a href="author.html#237">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000238.html 9 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration" </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"</H1> <B>Brian Long</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22&In-Reply-To=%3C8DBDC6D514F3F44B99EA56F331381FE1C32E721C%40mailbox10.lucas.alllucas.com%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"">blong at skysound.com </A><BR> <I>Tue Nov 4 09:50:19 MST 2014</I> <P><UL> <LI>Previous message: <A HREF="000237.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000239.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#238">[ date ]</a> <a href="thread.html#238">[ thread ]</a> <a href="subject.html#238">[ subject ]</a> <a href="author.html#238">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>Please advise on where the papers should be posted and I will make them available from SMPTE via the liaison. There are a number of reference works in the AES Digital Cinema and Television TC reflector. The statement below is correct: "A "typical" cinema - in the 1970s this meant between approximately 200 and 2000 seats with the typical reverberation characteristics of a vaudeville theatre;" Unfortunately few cinemas retain characteristics such as this in the modern age. However the practice of referring to the X Curve remains the status quo and was never changed. As a result you have in the modern age a great number of screens with much less reverberant characteristics that still refer to the X Curve. Whether they should still be calibrated to the X Curve or not is an entirely different discussion which will happen in the next phase of work in SMPTE. However with the matter at hand it is interesting to note a few things that were examined and discussed extensively in this work: In a modern cinema with an approximate acoustic near or in the THX specification window RTA, fixed FFT transfer functions, and multi time window FFT based transfer functions returned nearly identical results when nuisance variables were eliminated. This was proven in a scenario examined by the SMPTE group in a modern cinema where devices shared the same electrical path from microphones to pre amplifiers along the same cables and then were split to a variety of devices from major manufacturers that are readily available. Differences in measurements were found to be attributed to various device specific characteristics sampling rates, measurement bins, etc. Such differences were minor. The results of this testing are on the SMPTE group's to do list to be formed into a publishable document and study. In combination with companion work that was detailed in reference papers presented at various conferences it was shown that the X Curve as found today in modern cinemas is primarily a result of screen and loudspeaker interaction with room acoustics and air attenuation in the majority of modern cinema environments being relatively minor contributing factors. It should be noted that the work in SMPTE and by other parties was done with the input of those originally responsible for the X-Curve. Please let me know if additional clarification of the work that led to this document is needed. Regards, Brian Long -----Original Message----- From: <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A> [mailto:<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A>] On Behalf Of markyonge Sent: Tuesday, November 04, 2014 6:32 AM To: Working group on Measurement and equalization of sound systems in rooms Cc: markyonge Subject: Re: [SC-04-08] Comments on "SMPTE-Modern-Calibration" Dear SC-04-08, This discussion of the SMPTE ST 202 X-curve, developed in the late 1970s, would only be of arcane historical interest, except for the suggestion that it might be perpetuated in the Modern Calibration draft using a different measurement technique. In the late 1970s I aligned many cinemas for Dolby Laboratories, who were active in developing the X-curve as a pragmatic tool to calibrate the B-chains of mix rooms and cinemas. The intent was to take full advantage of the essentially-flat A-chain frequency response in Dolby Stereo films. The measurement equipment that was available seemed like rocket science at the time, but now looks very dated. The measurement technique produced reasonably consistent results, but relied heavily on some working assumptions, many of which are also now outdated. The following assertions are fully supported by SMPTE ST 202:2010 (and its close cousin, ISO 2969). I am happy to go into this in more detail, developing the presentation I gave to SC-04-08 in Rome, May 2013. Meanwhile: • The purpose of the X-curve is to predict a flat frequency response for direct (first-arrival) sound; • The X-curve is a measurement artifact and not an audio roll-off; • The X-curve represents a display on a real-time audio analyser (RTA), comprising a flat spectral component of the direct sound overlaid at lower frequencies by a higher-amplitude reverberation contribution from the cinema auditorium. (The direct sound comprises instantaneous energy at the microphone, while the reverberant energy has been integrating for perhaps as long as a second in a "typical" cinema, building up to a higher amplitude). The X-curve is directly useful ONLY under the following circumstances: • A "typical" cinema - in the 1970s this meant between approximately 200 and 2000 seats with the typical reverberation characteristics of a vaudeville theatre; • Continuous pink noise - other stimuli exist that will not produce the same reverberation component and will not produce a satisfactory X-curve display; • 1/3-octave real-time audio analyser (RTA). The X-curve is NOT useful under the following circumstances: • Small cinemas, screening rooms, preview theatres, music studio control rooms, home theatres; • Very large cinemas; • Open-air cinemas, sports stadia; • Any cinema acoustically treated to reduce its reverberation; • Discontinuous test signals; • Any spectrum-analysis tool that isn't a 1/3-octave RTA. In such circumstances where the X-curve is not useful, the X-curve should be ignored and the best available measurement technique should be used to produce a flat frequency response for direct (first-arrival) sound arriving at a typical audience position. Let me be clear: An auditorium equalised to the X-curve inappropriately is very likely to lack high-frequency energy and will sound dull. I do not believe that references to the X-curve should be continued in this Modern Calibration draft now that the measurement tools and cinema acoustics have changed sufficiently to take its application out of the main stream - it is, in effect, obsolete. Correspondence on this reflector has invoked various alternative explanations for the X-curve, referring to external papers unavailable to this group. If these papers contain some engineering wisdom relevant for this discussion, then it would be appropriate to post those papers to this group AND to identify the relevant text with reference to the corresponding clause numbers in ST 202. A bit of rigour would be appropriate - as engineers, we have a duty to keep science and folklore separate. Sincerely, Mark Yonge vice chair, SC-04-08 _______________________________________________ SC-04-08 mailing list <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">SC-04-08 at standards.aes.org</A> <<A HREF="http://standards.aes.org/sc.cfm?ID=91">http://standards.aes.org/sc.cfm?ID=91</A>> </PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000237.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000239.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#238">[ date ]</a> <a href="thread.html#238">[ thread ]</a> <a href="subject.html#238">[ subject ]</a> <a href="author.html#238">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000239.html 9 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration" </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"</H1> <B>philip newell</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22&In-Reply-To=%3CCAEEhACn_7fCiFh_3n7-HXQmW4cxGig%3DtjM9Nr3Z33ZXR1Jsj_g%40mail.gmail.com%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"">philiprnewell at gmail.com </A><BR> <I>Tue Nov 4 10:29:30 MST 2014</I> <P><UL> <LI>Previous message: <A HREF="000238.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000240.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#239">[ date ]</a> <a href="thread.html#239">[ thread ]</a> <a href="subject.html#239">[ subject ]</a> <a href="author.html#239">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>Dear Mark, I have inserted some comments in you text, below. The statements can all be corroborated by published evidence. Best wishes, Philip On 4 November 2014 15:31, markyonge <<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">mark.yonge at aes.org</A>> wrote: ><i> Dear SC-04-08, </I>><i> </I>><i> This discussion of the SMPTE ST 202 X-curve, developed in the late 1970s, </I>><i> would only be of arcane historical interest, except for the suggestion that </I>><i> it might be perpetuated in the Modern Calibration draft using a different </I>><i> measurement technique. </I>><i> </I>><i> In the late 1970s I aligned many cinemas for Dolby Laboratories, who were </I>><i> active in developing the X-curve as a pragmatic tool to calibrate the </I>><i> B-chains of mix rooms and cinemas. The intent was to take full advantage of </I>><i> the essentially-flat A-chain frequency response in Dolby Stereo films. The </I>><i> measurement equipment that was available seemed like rocket science at the </I>><i> time, but now looks very dated. The measurement technique produced </I>><i> reasonably consistent results, but relied heavily on some working </I>><i> assumptions, many of which are also now outdated. </I>><i> </I>><i> The following assertions are fully supported by SMPTE ST 202:2010 (and its </I>><i> close cousin, ISO 2969). I am happy to go into this in more detail, </I>><i> developing the presentation I gave to SC-04-08 in Rome, May 2013. Meanwhile: </I>><i> </I>><i> • The purpose of the X-curve is to predict a flat frequency response </I>><i> for direct (first-arrival) sound; </I>><i> </I> It *patently does not do this, as has been shown in the recent SMPTE report (and the referenced Cardiff IOA paper).* ><i> • The X-curve is a measurement artifact and not an audio roll-off; </I>><i> </I> *It is an audio roll-off.* ><i> • The X-curve represents a display on a real-time audio analyser </I>><i> (RTA), comprising a flat spectral component of the direct sound overlaid at </I>><i> lower frequencies by a higher-amplitude reverberation contribution from the </I>><i> cinema auditorium. (The direct sound comprises instantaneous energy at the </I>><i> microphone, while the reverberant energy has been integrating for perhaps </I>><i> as long as a second in a "typical" cinema, building up to a higher </I>><i> amplitude). </I>><i> </I> *The evidence does not support ths conclusion. * ><i> </I>><i> The X-curve is directly useful ONLY under the following circumstances: </I>><i> • A "typical" cinema - in the 1970s this meant between approximately </I>><i> 200 and 2000 seats with the typical reverberation characteristics of a </I>><i> vaudeville theatre; </I>><i> • Continuous pink noise - other stimuli exist that will not produce </I>><i> the same reverberation component and will not produce a satisfactory </I>><i> X-curve display; </I>><i> • 1/3-octave real-time audio analyser (RTA). </I>><i> </I> *All of this is questionable. * ><i> </I>><i> The X-curve is NOT useful under the following circumstances: </I>><i> • Small cinemas, screening rooms, preview theatres, music studio </I>><i> control rooms, home theatres; </I>><i> </I> *Correct, but in reality, it is used in many of these rooms.* ><i> • Very large cinemas; </I>><i> • Open-air cinemas, sports stadia; </I>><i> • Any cinema acoustically treated to reduce its reverberation; </I>><i> </I> *Dolby (and others) apply it in rooms of all decay times, as shown in the SMPTE report.* ><i> • Discontinuous test signals; </I>><i> • Any spectrum-analysis tool that isn't a 1/3-octave RTA. </I>><i> </I> *The evidence does not support this. * ><i> </I>><i> In such circumstances where the X-curve is not useful, the X-curve should </I>><i> be ignored and the best available measurement technique should be used to </I>><i> produce a flat frequency response for direct (first-arrival) sound arriving </I>><i> at a typical audience position. </I>><i> </I>><i> Let me be clear: An auditorium equalised to the X-curve inappropriately is </I>><i> very likely to lack high-frequency energy and will sound dull. </I>><i> </I> *As do most cinemas, because they are aligned to the X-curve. * ><i> </I>><i> I do not believe that references to the X-curve should be continued in </I>><i> this Modern Calibration draft now that the measurement tools and cinema </I>><i> acoustics have changed sufficiently to take its application out of the main </I>><i> stream - it is, in effect, obsolete. </I>><i> </I> *Dolby (and others) still apply it in rooms of all decay times, as shown in the SMPTE report.* ><i> </I>><i> Correspondence on this reflector has invoked various alternative </I>><i> explanations for the X-curve, referring to external papers unavailable to </I>><i> this group. If these papers contain some engineering wisdom relevant for </I>><i> this discussion, then it would be appropriate to post those papers to this </I>><i> group AND to identify the relevant text with reference to the corresponding </I>><i> clause numbers in ST 202. </I>><i> </I> <A HREF="https://www.smpte.org/standards/reports">https://www.smpte.org/standards/reports</A> * B-Chain Frequency and Temporal Response Analysis of Theatres and Dubbing Stages* ><i> </I>><i> A bit of rigour would be appropriate - as engineers, we have a duty to </I>><i> keep science and folklore separate. </I>><i> </I>><i> Sincerely, </I>><i> </I>><i> Mark Yonge </I>><i> vice chair, SC-04-08 </I>><i> _______________________________________________ </I>><i> SC-04-08 mailing list </I>><i> <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">SC-04-08 at standards.aes.org</A> </I>><i> <<A HREF="http://standards.aes.org/sc.cfm?ID=91">http://standards.aes.org/sc.cfm?ID=91</A>> </I></PRE> <!--endarticle--> <HR> <P><UL> <!--threads--> <LI>Previous message: <A HREF="000238.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000240.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#239">[ date ]</a> <a href="thread.html#239">[ thread ]</a> <a href="subject.html#239">[ subject ]</a> <a href="author.html#239">[ author ]</a> </LI> </UL> <hr> <a href="https://secure.aes.org/mailman/listinfo/sc-04-08">More information about the SC-04-08 mailing list</a><br> Expand 000240.html 9 KB HTML - Click to view Options Copy Download Link <TITLE> [SC-04-08] Comments on "SMPTE-Modern-Calibration" </TITLE> pre { white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ } <H1>[SC-04-08] Comments on "SMPTE-Modern-Calibration"</H1> <B>Pete Soper</B> <A HREF="mailto:sc-04-08%40standards.aes.org?Subject=Re%3A%20%5BSC-04-08%5D%20Comments%20on%20%22SMPTE-Modern-Calibration%22&In-Reply-To=%3C2BE563BCBE473946A8E72AE261D4F64B0177FD82D8%40XCHG1.ms.msli.com%3E" TITLE="[SC-04-08] Comments on "SMPTE-Modern-Calibration"">psoper at meyersound.com </A><BR> <I>Tue Nov 4 11:03:07 MST 2014</I> <P><UL> <LI>Previous message: <A HREF="000239.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI>Next message: <A HREF="000241.html">[SC-04-08] Comments on "SMPTE-Modern-Calibration" </A></li> <LI> <B>Messages sorted by:</B> <a href="date.html#240">[ date ]</a> <a href="thread.html#240">[ thread ]</a> <a href="subject.html#240">[ subject ]</a> <a href="author.html#240">[ author ]</a> </LI> </UL> <HR> <!--beginarticle--> <PRE>Regardless of any individuals perceived/believed/rumored rationale behind the X-curve, the fact remains that it is still the prescribed response plot for audio frequency response in ST-202M and RP-200 which are still the current SMPTE standard documents and practices for cinema B-chain alignment and calibration. The objective of the modern calibration AHG is not to re-write these standards, but rather to provide guidelines for using more commonly available modern measurement tools and techniques such as dual channel FFT transfer function analysis in performing the setup and verification of systems in accordance with SMPTE 202M and RP-200. As such, any arguments for or against the X-curve are completely outside the scope of that group- and correspondingly, AES X215. However, with that said- I think it is important to point out that several recent studies have illustrated that the matter of needing sound to project through a perforated screen results in a nominally "flat" speaker behind the screen results in very close to an "X-curve" response in front of the screen, this net effect on system response is repeatable and verifiable with either 1/3 octave RTA or dual channel transfer function analysis and despite claims by many to the contrary- is NOT just a measurement artifact, it is simply what happens when sound is transmitted through a perforated barrier. The recently published B-chain theater test group report shows that only one of the dubbing stages having a woven fabric screen (as opposed to perforated solid material) required a low-order HF roll off be imposed to meet the X-curve target, all of the perforated screen systems in the study had either no significant HF equalization or actually required boosting of some high frequencies in order to comply with the X-curve target window. -Pete Soper Meyer Sound Laboratories Inc. -----Original Message----- From: <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A> [mailto:<A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">sc-04-08-bounces at standards.aes.org</A>] On Behalf Of markyonge Sent: Tuesday, November 04, 2014 6:32 AM To: Working group on Measurement and equalization of sound systems in rooms Cc: markyonge Subject: Re: [SC-04-08] Comments on "SMPTE-Modern-Calibration" Dear SC-04-08, This discussion of the SMPTE ST 202 X-curve, developed in the late 1970s, would only be of arcane historical interest, except for the suggestion that it might be perpetuated in the Modern Calibration draft using a different measurement technique. In the late 1970s I aligned many cinemas for Dolby Laboratories, who were active in developing the X-curve as a pragmatic tool to calibrate the B-chains of mix rooms and cinemas. The intent was to take full advantage of the essentially-flat A-chain frequency response in Dolby Stereo films. The measurement equipment that was available seemed like rocket science at the time, but now looks very dated. The measurement technique produced reasonably consistent results, but relied heavily on some working assumptions, many of which are also now outdated. The following assertions are fully supported by SMPTE ST 202:2010 (and its close cousin, ISO 2969). I am happy to go into this in more detail, developing the presentation I gave to SC-04-08 in Rome, May 2013. Meanwhile: • The purpose of the X-curve is to predict a flat frequency response for direct (first-arrival) sound; • The X-curve is a measurement artifact and not an audio roll-off; • The X-curve represents a display on a real-time audio analyser (RTA), comprising a flat spectral component of the direct sound overlaid at lower frequencies by a higher-amplitude reverberation contribution from the cinema auditorium. (The direct sound comprises instantaneous energy at the microphone, while the reverberant energy has been integrating for perhaps as long as a second in a "typical" cinema, building up to a higher amplitude). The X-curve is directly useful ONLY under the following circumstances: • A "typical" cinema - in the 1970s this meant between approximately 200 and 2000 seats with the typical reverberation characteristics of a vaudeville theatre; • Continuous pink noise - other stimuli exist that will not produce the same reverberation component and will not produce a satisfactory X-curve display; • 1/3-octave real-time audio analyser (RTA). The X-curve is NOT useful under the following circumstances: • Small cinemas, screening rooms, preview theatres, music studio control rooms, home theatres; • Very large cinemas; • Open-air cinemas, sports stadia; • Any cinema acoustically treated to reduce its reverberation; • Discontinuous test signals; • Any spectrum-analysis tool that isn't a 1/3-octave RTA. In such circumstances where the X-curve is not useful, the X-curve should be ignored and the best available measurement technique should be used to produce a flat frequency response for direct (first-arrival) sound arriving at a typical audience position. Let me be clear: An auditorium equalised to the X-curve inappropriately is very likely to lack high-frequency energy and will sound dull. I do not believe that references to the X-curve should be continued in this Modern Calibration draft now that the measurement tools and cinema acoustics have changed sufficiently to take its application out of the main stream - it is, in effect, obsolete. Correspondence on this reflector has invoked various alternative explanations for the X-curve, referring to external papers unavailable to this group. If these papers contain some engineering wisdom relevant for this discussion, then it would be appropriate to post those papers to this group AND to identify the relevant text with reference to the corresponding clause numbers in ST 202. A bit of rigour would be appropriate - as engineers, we have a duty to keep science and folklore separate. Sincerely, Mark Yonge vice chair, SC-04-08 _______________________________________________ SC-04-08 mailing list <A HREF="https://secure.aes.org/mailman/listinfo/sc-04-08">SC-04-08 at standards.aes.org</A> <<A HREF="http://standards.aes.org/sc.cfm?ID=91">http://standards.aes.org/sc.cfm?ID=91</A>> NOTICE: This email may contain confidential information. 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