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Dan Lavry · 1st July 2009

I re read the first post, but I am an engineer and a gear designer an I live in the real world, as most of you guys.

The first post is about dither and noise shaping. That kind of a process is there for word length reduction (to overcome low level signal quantization distortions and noise modulation). The CD format is 16 bits, so there are times when we need reduce word length. When one adds dither (with or without noise shaping), the noise level goes up, so it is not an improvment in SNR, it is a trade off between
more noise and less distortions and noise modulation of low level signals.

But the process of archiving or music and the released in 88.2-96KHz few "real world" formats does not require dither and noise shaping. Why trade off if you do not have to?

But let me try an go along with the theoretical concept here for a moment. If one has a system that is virtually noiseless, and the sample rate is say 88.2KHz, one can noise shape the signal perfectly (in theory). With an 88.2KHz system, the bandwidth is 44.1KHz, so take the noise and move it from under say 25KHz to the upper frequencies say 25Khz-44KHz. That is a huge range for noise shaping.

In the case of noise shaping a 44.1KHz, we move the noise from the frequency hearing sensitive range (such as 1-3KHz) into less sensitive range such as 14-22KHz. That upper range is still within the audible range. But at 88.2KHz-96KHz, we have a lot of extra non audible range to shape the noise into - plenty of room in fact.

So why go to higher sample rate then 88.2KHz? The noise shaping argument does not call for 100MHz range. Yes, in theory, one can have a real easy time moving all the noise if the sample rate was approaching infinity.

In fact, in theory, there is no down side to sampling at 1GHz, there is no theoretical limit to storage, to DSP speed, there is no real world noise and distortions.

One more time, we are faced with decisions that are best left to real world considerations, and much of it is about compromises that steer us toward optimal points.

Given that 88.2-96KHz yields enough theoretical and even practical range to noise shape outside the audio range, we can conclude that higher and higher sampling is not needed, thus the argument that higher sampling for better SNR should be put away.

Instead, we can say that high enough sampling such as 88.2-96KHz yields enough range to design a noise shaping capable of moving virtually all the noise from audible frquencies to higher inaudible frequencies.

I never thought I will see the day where Dither and SNR will become a factor in a discussion about the trade off between sample rate and SNR. Not even a theoretical discussion.

I view this as just one more attempt to support and rationalize higher sampling rate, and like the other various arguments, it ends up at 60-70KHz being the optimal rate. 60-70KHz yields enough range to park the unwanted truncated noise away to non audible range (say 22- 30KHz for a 60KHz sample rate).

regards

Dan Lavry
Lavry Engineering

1st July 2009	#43
Dan Lavry Gear addict Joined: May 2005 Posts: 437	I re read the first post, but I am an engineer and a gear designer an I live in the real world, as most of you guys. The first post is about dither and noise shaping. That kind of a process is there for word length reduction (to overcome low level signal quantization distortions and noise modulation). The CD format is 16 bits, so there are times when we need reduce word length. When one adds dither (with or without noise shaping), the noise level goes up, so it is not an improvment in SNR, it is a trade off between more noise and less distortions and noise modulation of low level signals. But the process of archiving or music and the released in 88.2-96KHz few "real world" formats does not require dither and noise shaping. Why trade off if you do not have to? But let me try an go along with the theoretical concept here for a moment. If one has a system that is virtually noiseless, and the sample rate is say 88.2KHz, one can noise shape the signal perfectly (in theory). With an 88.2KHz system, the bandwidth is 44.1KHz, so take the noise and move it from under say 25KHz to the upper frequencies say 25Khz-44KHz. That is a huge range for noise shaping. In the case of noise shaping a 44.1KHz, we move the noise from the frequency hearing sensitive range (such as 1-3KHz) into less sensitive range such as 14-22KHz. That upper range is still within the audible range. But at 88.2KHz-96KHz, we have a lot of extra non audible range to shape the noise into - plenty of room in fact. So why go to higher sample rate then 88.2KHz? The noise shaping argument does not call for 100MHz range. Yes, in theory, one can have a real easy time moving all the noise if the sample rate was approaching infinity. In fact, in theory, there is no down side to sampling at 1GHz, there is no theoretical limit to storage, to DSP speed, there is no real world noise and distortions. One more time, we are faced with decisions that are best left to real world considerations, and much of it is about compromises that steer us toward optimal points. Given that 88.2-96KHz yields enough theoretical and even practical range to noise shape outside the audio range, we can conclude that higher and higher sampling is not needed, thus the argument that higher sampling for better SNR should be put away. Instead, we can say that high enough sampling such as 88.2-96KHz yields enough range to design a noise shaping capable of moving virtually all the noise from audible frquencies to higher inaudible frequencies. I never thought I will see the day where Dither and SNR will become a factor in a discussion about the trade off between sample rate and SNR. Not even a theoretical discussion. I view this as just one more attempt to support and rationalize higher sampling rate, and like the other various arguments, it ends up at 60-70KHz being the optimal rate. 60-70KHz yields enough range to park the unwanted truncated noise away to non audible range (say 22- 30KHz for a 60KHz sample rate). regards Dan Lavry Lavry Engineering