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In Reply to: Re: Actually, no, i don't consider myself a Guru at all ... posted by andy_c on April 27, 2004 at 21:43:12:
look at it this way. using a 24 bit A/D converter record a musical signal with a low gain setting, such that the entire signal is completely encoded only in the lower 12 bits.the results would be no different if you had recorded the musical signal with a 12-bit A/D converter but at optimal gain setting.
actually, practically the results will be worse off than using a 12 bit A/D converter in the first place, since the lower bits of an A/D are typically less accurate and less linear than the upper bits.
you may ask - well, why record at such a low gain level? why not set the gain such that the signal is encoded using the full 24 bits?
the reason is if you are recording live, you have no way of knowing in advance what the maximum peak of the music will be, so you want to be conservative and set the gain at a level where you think is optimal, then back down a bit to leave some headroom just in case the music turned out to be louder than you think. even if you have a luxury of asking the orchestra to play the loudest passage so that you can calibrate gain beforehand, you still want to leave some headroom "just in case".
a symphony orchestra is the worst case scenario. a symphony can be at an average level of 70-80 dB SPL but suddenly peak all the way to 120 dB or more for the finale. the quandary is: what do you set the gain at? if you set the gain for 70-80dB the signal will surely clip at the end (big no no). if you set the gain low enough to handle the peak at the end then most of the time the music is being recorded at -50dB below max which means you are not using the full 24 bits of the A/D converter, you are using maybe the lower 16.
i find that DSD, being a 1-bit PDM, is better at capturing low level signals. i've heard some DSD recordings done at low gain that sounded much better than the equivalent PCM recording done at low gain. the goal is still to record with the gain as high as possible, but no higher.
i still stand by my assertion that good 24 bit PCM would probably have been done with 2-4 dB headroom, which means the "effective" resolution of the recording is only 20-22 bits, assuming a "perfect" A/D converter. normalization, followed by effects processing at 24 bits of course increase the apparent resolution, but doesn't completely hid the fact that the original tracks only have 20-22 bits used.
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Follow Ups
- Re: Actually, no, i don't consider myself a Guru at all ... - Christine Tham 23:07:00 04/27/04 (3)
- Re: Actually, no, i don't consider myself a Guru at all ... - andy_c 20:14:41 04/28/04 (2)
- Re: Actually, no, i don't consider myself a Guru at all ... - Christine Tham 20:27:20 04/28/04 (1)
- with the proper signal conditioning... - NonA 07:39:18 04/29/04 (0)
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