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Re: May not be undesirable

Posted by Todd Krieger (A) on December 6, 2006 at 00:17:11

In Reply to: Re: May not be undesirable posted by Dave Kingsland on December 5, 2006 at 11:05:30:

"The brick wall filter is at 22.05 KHz (all frequency samples >= 22.05 KHz are set to 0)."

I'm not sure what is meant by "frequency samples".... The samples occur in the time domain with digital audio.

"The purpose of converting to the higher sample rate is to move the player's filter out of the way, so it has no impact on the 'ideal' brick wall filter he implemented."

This is not exactly the case.... It moves the "first alias" (the unwanted ulrasonic image mirroring half the sample frequency) away from the audio band, which can then be filtered out with a gradual analog post filter (which follows the digital filter).

The conversion to a higher sample rate is an integral part of a digital filter.... The digital "brickwall" filter cannot even be done without such conversion.

"First, I have trouble understanding why pre-ringing would be any more or less audible than post-ringing, especially in a complex musical signal."

Since the decays (energy trailing the transient) in music are generally "longer" in duration than the attacks (energy ahead of the transient), I think post-ringing would be less-noticeable than pre-ringing.

"Finally, I'm not necessarily convinced the ringing is even the right thing to focus on. A more gentle filter not only reduces ringing but also softens the attack of transients."

This this backwards.... And it may initially seem counter-intuitive.... It actually sharpens the attacks on transients..... A gentle filter in frequency indeed equates to a less ringing, which means faster time response. The ringing itself is what softens transients. The focus on such filters is the time response- Which happens to provide a "gentle" slope characteristic in frequency.

I do agree that the ringing isn't the most-important thing to focus on..... RFI and attenuating it should be the primary focus. For I think the sonic degradation from RFI is far worse than the degradation from the ringing of a brickwall digital filter.

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

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