33AndAThird
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- Dec 30, 2023
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Hi all,
I listened to the Darko Audio podcast 10 hi-fi myths busted with Peter Comeau, and have questions about the first myth "Hi-res audio sounds better because of its ultrasonic content". I figured this would be the best place to get some straight, evidence based answers I know there will be some eye-rolls as to the source, but my questions stem from wanting to understand.
Peter Comeau starts out by confirming what we all know to be true, which is that anything above 20KHz is inaudible and the proposition that one can get a better musical experience by reproducing frequencies above 20KHz is nonsense. He then went on to say that hi-res does indeed sound better not because of reproducing higher frequencies but that the filter is well into the ultrasonic region and hence not audible. He gives the example of early CD players having a brick-wall filter at 20KHz and that being detrimental to performance.
My questions are:
1. Why is a filter required in the first place? I superficially understand Nyquist, and that a 10KHz signal will also reproduce a 34.1KHz alias signal when converting back to analog, but why do we care? If we can't hear it, and likely the equipment can't reproduce it anyway, why do we need to bother with a reconstruction filter that shops off everything above 20KHz?
2. On the assumption that the filter is required, why is a brickwall filter range a bad thing compared to others? Peter talks about the issue being in the time domain, and that the 20KHz brickwall filter of the early CD days had both pre and post echoes. He said that this can be viewed on an oscilloscope and the evidence is online (I couldn't find it but its entirely possible I'm using the wrong terminology). Is there evidence to suggest a brickwall is a bad thing, and why do we get artifacts in the time domain?
3. The summary given is "By having a higher sample rate, your filter is moved further away from the upper limit of the audible band, so it doesn't trouble as much the time-domain response of the signal". Presumably this means that any filter, brickwall or not, has a negative impact to some degree and we should avoid them in the audible range. Is there evidence for this?
Any help in answering my questions is much appreciated! Thanks
I listened to the Darko Audio podcast 10 hi-fi myths busted with Peter Comeau, and have questions about the first myth "Hi-res audio sounds better because of its ultrasonic content". I figured this would be the best place to get some straight, evidence based answers I know there will be some eye-rolls as to the source, but my questions stem from wanting to understand.
Peter Comeau starts out by confirming what we all know to be true, which is that anything above 20KHz is inaudible and the proposition that one can get a better musical experience by reproducing frequencies above 20KHz is nonsense. He then went on to say that hi-res does indeed sound better not because of reproducing higher frequencies but that the filter is well into the ultrasonic region and hence not audible. He gives the example of early CD players having a brick-wall filter at 20KHz and that being detrimental to performance.
My questions are:
1. Why is a filter required in the first place? I superficially understand Nyquist, and that a 10KHz signal will also reproduce a 34.1KHz alias signal when converting back to analog, but why do we care? If we can't hear it, and likely the equipment can't reproduce it anyway, why do we need to bother with a reconstruction filter that shops off everything above 20KHz?
2. On the assumption that the filter is required, why is a brickwall filter range a bad thing compared to others? Peter talks about the issue being in the time domain, and that the 20KHz brickwall filter of the early CD days had both pre and post echoes. He said that this can be viewed on an oscilloscope and the evidence is online (I couldn't find it but its entirely possible I'm using the wrong terminology). Is there evidence to suggest a brickwall is a bad thing, and why do we get artifacts in the time domain?
3. The summary given is "By having a higher sample rate, your filter is moved further away from the upper limit of the audible band, so it doesn't trouble as much the time-domain response of the signal". Presumably this means that any filter, brickwall or not, has a negative impact to some degree and we should avoid them in the audible range. Is there evidence for this?
Any help in answering my questions is much appreciated! Thanks