Quote:
Originally Posted by Alexey Lukin  Robin, I believe that the original quote by Bob Katz is made about a dithered PCM system, however it still holds true for a non-dithered PCM system. When quantizing a signal at a higher sampling rate, the quantization distortion (or dithering noise) has the same power (defined by the amplitude of the least-significant bit), but their spectrum is spread over a wider frequency range. If we are only interested in noise (or distortion) levels in the limited audible range, their levels (and power spectrum density) drop when higher sampling rate is used. |
Hi Alexey,
thanks for trying to help me out here. I still don't understand. Wouldn't the harmonics build up evenly across the frequency range, generating the same energy in a given frequency range (such as the audible spectrum), regardless of sample rate? Or am I confusing cause and effect?
Furthermore, I tried to test this using the following set up:
- start with a (complex audio) 24/96 recording
- applied a 4-pole low-pass at 1kHz and dropped audio level by 60 dB (to make subsequent harmonic distortion more obvious)
- made two versions, one SRed to 192 kHz, one SRed to 44.1 kHz.
- both versions were then saved (truncated) to 16 bits.
- applied 60 dB of gain to both versions (to make results audible)
- applied a 4-pole high-pass filter at 5kHz, so that pretty much only distortion products are left.
- measured levels
The resulting quantization distortion measures (near as makes no difference) the same in both files. Actually, the 44.1 version even measures a teeny bit lower. If I read your post correctly, the higher sample rate file's quantization distortion should measure considerably lower. Is there a flaw in my test setup?
EDIT: I just realized the flaw in my setup... I didn't downsample the 192kHz file after truncation. Doh. After doing so, there is now indeed a difference in total distortion level. Albeit significantly less than expected, nowhere near 6 dB. But it comfirms there is or can be AT LEAST SOME difference depending on SR.