[BC] CD vs LP

[Robert Orban]

At 08:00 AM 9/22/2008, Rich Wood wrote:
>Some syndicators used to claim that duplicating tape backwards 
>improved quality because it reversed the waveform so you didn't have 
>to worry about high energy peaks.

Actually, what this technique does is to cancel part of the group 
delay distortion inherent in the analog tape record/playback process. 
It's similar to an offline trick one can do to make IIR digital 
filters that have no group delay distortion at all -- pass the signal 
through one filter, reverse the output file, and pass it through the 
same filter again. The resulting magnitude response is what you would 
expect (the sum of the two filters' magnitude responses if you 
express these in dB) but the group delay distortion cancels completely.

Bob Orban