16 bit vs 24 bit
Reply #23 – 2006-11-15 13:16:13
First you would have to demonstrate the audibility of quantization noise in 16 bit/44.1kHz stuff to find any excuse to go to a higher sampling rate. I don't have to do anything. I didn't claim that higher sampling rates are needed -- just that lower sample resolutions can be used at higher sampling rates to get the same SNR performance in the audible band. I commented because everyone was only talking about bits/sample and not about samples/second. That's all.Even a simple 4th order IIR filter ... I don't know what you are writing about. What are the parameters of such a filter (filter variety, cutoff, highpass/lowpass/band pass/, transition bandwidth, etc)? What is it filtering out? Is it hardware or software? Where might it be employed? If it does something useful, why is it not in normal use? I'm talking about noise shaping filters . These filters are usually applied in conjunction with dithering while a signal is requantized in software (ie from 24 to 16 bits) to shape the quantization noise spectrally. See this thread , download noise.zip and checkout the sym20.sos filter. If you feel like plotting its response in Matlab: Here's what you should do:sos = [ 1.0 -0.6160081826103387 0.7225 1.0 0.8253356149096804 0.25 1.0 -0.8253356149096804 0.25 1.0 0.6160081826103387 0.7225 ]; [b,a] = sos2tf(sos); freqz(b,a); This is a screenshot of the filter design tool showing the filter's response on a logarithmic amplitude scale (Y-axis, each horizontal line = 10 dB, the bright line correspondes to 0 dB) and linear frequency axis (X-axis, 0..nyguist frequency). If you requantize 24/96 to 16/96 using this filter you can still have a SNR of above 110 dB below 19 kHz -- not just 90 dB. If you use the sym30.sos filter instead you can go down to 12 bits/sample and have an SNR of 102 dB below 19 kHz and the PCM data rate would be equal to the rate you need for 24/48. Cheers! Sebastian