Re: [Sursound] Sursound Digest, Vol 68, Issue 17
Hi, Surely the best approach is to feed the noise signal (post decoder) into each speaker channel in turn and adjust the amplification on each channel until the level measured at the centre listening point is the same for each speaker. The panning approach won't work, as all speakers would be excited at various different levels. It would be useful after the above calibration to see if the sound of the noise of the noise was consistent everywhere everywhere it was panned. Ciao, Dave From: Iain Mott m...@reverberant.com Date: 18 March 2014 21:38:29 GMT To: Surround Sound discussion group sursound@music.vt.edu Subject: Re: [Sursound] calibrating ambisonic speakers using the k- system? Reply-To: m...@reverberant.com, Surround Sound discussion group sursound@music.vt.edu Em Tue, 2014-03-18 às 19:52 +, Fons Adriaensen escreveu: On Tue, Mar 18, 2014 at 03:32:55PM -0300, Iain Mott wrote: Thanks a lot Fons. When I pan pink noise with at W at -20dBFS RMS, the individual X and Y channels peak at about 3dB higher. Is that why you said to meter at 86dB and not 83? No. In a stereo system, with the levels as 0dB on the K-20 meter, each speaker produces 83 dB SPL. Assuming the signals are mostly decorrelated, the total level will be 86 dB. So the 'reference SPL' is 86 dB. OK - I see what you intended. For my current purposes, I'd like to reproduce as best as possible, ambiental b-format recordings over an array of speakers - and preferably try to match SPL measurements taken at each recording location. Do you think the formula above would be correct to match levels in this way? ie. if I make a recording at a site where the SPL is 70dB, during playback I meter this material (the W channel) at -13dB RMS on a k-20 meter, and in the case of a 14 channel system, calibrate each speaker channel at 71.5dB SPL (x = 83 - 10log14). Your only chance to get this right is to calibrate *via the decoder*. If you follow the procedure I explained, then 0 dB on the K-20 meter for W will corresponds to 86 dB SPL, no matter how the sound is distributed over the speakers. That's assuming you don't pan two or more strongly correlated signals to different directions (if you do that the result is no longer really Ambisonic). I now understand that W in the metering has a direct relationship to the total audio output of the array - no matter what the configuration - but sorry, I'm still in doubt as to how to go about adjusting the speaker output levels. I initially assumed that during the panning of the signal and the output adjustment, the speaker that is most in focus (at the peak level) would be soloed - but this wouldn't work because it wouldn't factor in the additional output from the other channels. Are you suggesting that all channels should be left open and the system tuned in a number of passes? Dare I say it: might the -10 log (N) level be a good starting point for each channel? Thanks -- next part -- An HTML attachment was scrubbed... URL: https://mail.music.vt.edu/mailman/private/sursound/attachments/20140319/7d24ab83/attachment.html ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Sursound Digest, Vol 68, Issue 17
On Wed, Mar 19, 2014 at 07:50:43PM +, Dave Hunt wrote: Surely the best approach is to feed the noise signal (post decoder) into each speaker channel in turn and adjust the amplification on each channel until the level measured at the centre listening point is the same for each speaker. That would be a prerequisite for the method I explained. But it still leaves you with an uncalibrated system, as the decoder gain (no matter how you define it) isn't included. The panning approach won't work, as all speakers would be excited at various different levels. It would be useful after the above calibration to see if the sound of the noise of the noise was consistent everywhere everywhere it was panned. On the contrary, it's the only one that will give the correct result. *** Calibration means to have a defined relation between *** the level of the W channel and the measured SPL. This can be done only with the decoder in the path. Another approach would be to sent W only (at reference level) to the decoder, and then measure each individual speaker (by soloing it, ambdec provides the function) and adjusting for reference SPL - 10 * log(number_of speakers). This would be less accurate as it doesn't allow for the partial correlation between speaker signals (which will depend on frequency if you use dual band decoding). Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Sursound Digest, Vol 68, Issue 17
On Wed, Mar 19, 2014 at 07:50:43PM +, Dave Hunt wrote: The panning approach won't work, as all speakers would be excited at various different levels. Anything to substantiate that claim ? Practice ? Theory ? FYI, I have used this method a number of times, with excellent results. I've also done the maths that show it do be correct. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Sursound Digest, Vol 68, Issue 17
Em Wed, 2014-03-19 às 20:21 +, Fons Adriaensen escreveu: Another approach would be to sent W only (at reference level) to the decoder, and then measure each individual speaker (by soloing it, ambdec provides the function) and adjusting for reference SPL - 10 * log(number_of speakers). This would be less accurate as it doesn't allow for the partial correlation between speaker signals (which will depend on frequency if you use dual band decoding). Great - yes, I was hoping this would work. The SPL meter arrived today by post - but i've still only two channels of amplification. Will test as soon as the equipment is organised. Thanks a lot for your help. Iain ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
