Thursday, May 18, 2017

Linear vs Minimum Phase

Here's a discussion about linear and minimum phase filters for digital to analog reconstruction.

The admin Ultrabike argues for linear phase...they produce the least phase distortion in the passband. He also argues away the obsession about pre-ringing as nonsense.  I think he makes a pretty good case.  The steepest and most linear phase filter is the most accurate one and the most transparent sounding (described by some as sounding hard, cold, "digital" or whatever).

Of course merely specifying linear phase says nothing about the particular rate or frequency involved.  Linear phase filters can be made to sound relatively warm just like minimum phase or NOS by making them slow.

This is strange, but apparently the more ultrasonics there are, the warmer things sound.  This "warmth" is mostly pseudorandom phase distortion, and that would be no surprise to electronic musicians.

My forthcoming Audio GD Master 7 Singularity Dac will have several Oversampling (OS) options, 8x, 4x, 2x, and (non-OS) NOS, and then combined with the NOS features of the NOS series of DAC's, which seem to include at least two different NOS flavors.  Previously these options were not available in the same DAC unit, but the latest firmware combined with recent hardware upgrades allows them to be.

With all this attention to NOS, I've been a little afraid the designer wasn't focusing enough on the OS designs, but at least he says the OS hasn't changed from the previous OS version(s) of the Master 7, which have been highly praised, so it won't be a step backwards.

From what I've seen above, I'm now not so worried that he doesn't seem to include minimum phase or "anodizing" options in the OS.  Plain old linear phase at 8x OS looks to be as good as anything.

I still wonder if Denon wasn't doing something special also with their AL24, which would appear to be some kind of up sampling, and how that relates to the above.  I'd always thought CD's sounded nice through Denon AL24 machines, even the ones using sigma delta conversion like the DVD 5900, and that was the first player in which I experienced superior sound from resampling the analog outputs rather than passing the digital directly to my DSPs.

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