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Jay-dub

Are there phase compensation filters available for '80's ACD's?

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I am especially interested in digital filters for recordings made with the Sony PCM1610, PCM1630, F1, and the Apogee filters that were installed aftermarket into certain PCM1610 units starting around 1986.

 

These older units used analog antialiasing filters, which could not be made phase-linear, and in some cases applied rather extreme "phase distortion" (phase delays to the very highest frequencies only). Digital recording units manufactured after around 1990 generally oversample and use a digital filter to prevent aliasing when downsampling to 44.1 kHz. These digital antialiasing filters, more often than not, are phase linear (symmetrical impulse response), and that is the sound I am accustomed to.

 

If I process an old recording with a matching filter, then the net result would be as if the original recording had been made with a phase-linear antialiasing filter. The appropriate digital filter should be straightforward to generate if we can find step-response data from these ADC's

 

Currently, when I listen to one of these old recordings, I put them through a lowpass filter to take out the the frequencies that are most affected by phase distortion (typical choice: 16kHz passband, 19kHz stopband). With phase compensation filters, I would listen with a couple more kilohertz of bandwidth.

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It would be enough to figure out specs for the analog low-pass to deal with that part. But always big question remains what happened to the recording after initial A/D conversion. Rarely things stop there and come out as such... Someone running bunch of eq, compressors, reverbs, etc...

 


Signalyst - Developer of HQPlayer

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