From a post I made in another thread, succeeding in confusing myself about the benefits (or lack thereof) of running conservative levels when recording a 24-bit word length. Any feedback from those with solid technical knowledge around my understanding as I describe it below? I have little confidenced I'm understanding this correctly, and would appreciate any guidance people may offer.
Can you explain how added dynamic range allows you to run levels more conservative? I'm not questioning the statement, I'm just trying to learn.
I'll try.
Although as I think through it again, it no longer makes sense. At least not for 24-bit listening. It may still make sense for 16-bit listening. Here we go...
In an ideal world, we use all 24-bits of resolution, a full 144 dB of dynamic range. Since 1 bit = 6 dBFS, the relationship between dBFS (our levels) and resolution (our bit-depth) looks like below, where S = signal and N = noise. In this ideal case, if we set our levels to peak basically at 0 dBFS, we use all 24-bits of resolution, the full 144 dB of dynamic range. The data is pure signal (no noise):
| -144 | -132 | -120 | -108 | -96 | -84 | -72 | -60 | -48 | -36 | -24 | -12 | 00 | dBFS
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| 24 | 22 | 20 | 18 | 16 | 14 | 12 | 10 | 08 | 06 | 04 | 02 | 00 | Bit-Depth
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|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS| Noise / SignalHowever, none of our preamps and ADCs achieve full 24-bits of resolution - too much self-noise. For the sake of discussion, let's assume that our preamp and ADC provides 108 dB of dynamic range, which equates to 18-bits of resolution. Everything below -108 dBFS is noise, i.e. all the data in the least significant 6-bits is noise. The new graph - again assuming our levels are effectively peaking at 0 dBFS - looks like the following, where S = signal and N = noise:
| -144 | -132 | -120 | -108 | -96 | -84 | -72 | -60 | -48 | -36 | -24 | -12 | 00 | dBFS
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| 24 | 22 | 20 | 18 | 16 | 14 | 12 | 10 | 08 | 06 | 04 | 02 | 00 | Bit-Depth
============================================================================================
|NNNNNN|NNNNNN|NNNNNN|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS| Noise / SignalNow let's assume we change our levels to peak at -6 dBFS. Since the noise-floor hasn't changed, we've now effectively reduced our resolution by 1-bit. The new graph looks thus:
| -144 | -132 | -120 | -108 | -96 | -84 | -72 | -60 | -48 | -36 | -24 | -12 | 00 | dBFS
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| 24 | 22 | 20 | 18 | 16 | 14 | 12 | 10 | 08 | 06 | 04 | 02 | 00 | Bit-Depth
============================================================================================
|NNNNNN|NNNNNN|NNNNNN|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSSSSS|SSS...| Noise / SignalIn this light, let's examine two qualifications of my previous statement (and one I've seen repeated often by others):
If our target listening resolution is 16-bit, we're in good shape - we're still capturing 17-bits of resolution, i.e. > 16-bits of resolution. This assumes, though, that 17-bit resolution dithered down to 16-bit sounds the same as 18-bit resolution dithered down to 16-bit. It also assumes any editing we perform does not benefit audibly from the extra 1-bit of resolution 18-bit provides v. 17-bit, prior to dithering down to 16-bit (or if there is an audible benefit, dithering down to 16-bit negates it).
If our target listening resolution is 24-bit (meaning an
actual bit-depth of 18-bit), we're actually reducing our resolution from 18- to 17-bits. Given that I hear a significant audible difference between 18- and 16-bit resolution, I'm inclined to say there's a significant audible difference between 17-bit and 16-bit (half of the difference between 18- and 16-bit). I have not performed any specific testing of this suggestion, however.
Anyway...all this leads me to believe my previous conceptions were incorrect, and that we should run our levels as close to 0 dBFS as possible regardless of the final target resolution, but especially if our final target resolution is "24-bit".
But I'm not 100% certain my understanding above is correct.
Anyone with more detailed technical knowledge able to chime in?FWIW, two posts with lots more info regarding levels, other reasons why one may or may not want to run them hot (mixing with other channels, finding the sweetspot in your analog gear), etc.:
http://taperssection.com/index.php/topic,58384.msg906769.html#msg906769http://taperssection.com/index.php/topic,58384.msg898317.html#msg898317