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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: Re: A lot of people don't understand dither posted by Christine Tham on March 2, 2007 at 14:30:28:
A good mic, mic pre amp and analog console have dynamic range of around 130dB. A good ADC will have dynamic range slightly exceeding 20 bits.So, the noise floor of electronics alone are too low to produce self dithering when truncating from 24 to 20.
Let's consider the case of "self dithering" caused by ambient background noise during recording. As far as I know, this is a "myth" and I'm not sure many engineers still believe in this. Let me explain why.
Typical peak levels in a live recording: 120dB SPL. Typical ambient noise in a live recording (assuming a concert hall) - around 40-50dB SPL. I have measured far worse, often due to air conditioning.
Typical peak levels in a studio: 100-110dB SPL. Typical ambient noise in a quiet studio: 20-30dB SPL. Again, I have measured studios that are worse (well, mine for instance :-))
These are all numbers based on my experience. Feel free to validate them yourself.
Assuming that we set the levels such that peak is close to 0dBFS, then typical noise level in a recording: around -70-80dB.
You can actually validate this yourself by doing an analysis of commercial recordings. The majority of them will exhibit ambient noise levels at these levels.
These levels are clearly too high to produce a self-dithering effect when truncating from 24 to 20. Particularly when you analyze the spectrum of the ambient noise and realize it is not random.
And in any case you can prove it to yourself. Take a recording with ambient noise at say -70dB. You will find you can easily hear a reverb tail even when it's amplitude is below -70dB.
Even in the best case scenario, noise levels may be at -90-100dB. This may potentially produce a "self dithering" effect for a 16-bit recording, but it won't for a 24-bit recording (with between 20-22 bits effective resolution).
You don't have to believe anything I say, but the numbers kind of speak for themselves, and they are numbers you can easily validate yourself.
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Follow Ups
- More on "self dithering" and actual noise levels in recordings - Christine Tham 15:46:57 03/02/07 (4)
- Re: More on "self dithering" and actual noise levels in recordings - Todd Krieger 00:36:14 03/08/07 (1)
- Re: More on "self dithering" and actual noise levels in recordings - Christine Tham 14:19:47 03/08/07 (0)
- Re: More on "self dithering" and actual noise levels in recordings - Dave Kingsland 17:05:52 03/03/07 (1)
- Re: More on "self dithering" and actual noise levels in recordings - Christine Tham 02:29:52 03/04/07 (0)
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