Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

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RE: Anagram Tech. ATF 24/192 Mk2 processor

Posted by flood2 (A) on March 24, 2020 at 16:58:04

In Reply to: RE: Anagram Tech. ATF 24/192 Mk2 processor posted by Todd Krieger on March 23, 2020 at 18:43:37:

They are no longer involved in audio AFAIK. There was no Anagram "Processor" as such - they only do software. The OP's tech gave a vague diagnosis by saying that he had traced the fault to the "Anagram chip". He could mean the ROM (unlikely) or the DSP. The software is designed to run on an Analog Devices SHARC or Blackfin DSP.
True upsampling would be D/A at the original sample rate followed by A/D at the new sample rate. This isn't how early hardware SRCs worked. They used lookup tables of pre-determined filter coefficients and linear interpolation to calculate the required filter coefficients depending on the ratio required. Calculated output samples are thus subject to an error. Jitter in the clock introduces a time related offset to the output sample and this shifts the calculated samples with respect to each other which increases distortion further from the distortion related to interpolation error.

The advantage of Q5 Upsampling (which was the trademarked name for the algorithm) was that they used polynomial interpolation which reduces the error in the new sample amplitude compared to what the "original" waveform would yield. Any clock jitter affecting the output sample spacing would have less of an effect.
My original Sony XA30ES had a similar filter option which used a Spline fit albeit without upsampling. Comparing this filter to the others yielded noticeably better imaging and very analogue smooth sound, but sounded oddly synthetic.

I have several versions on my Cambridge Audio 850C (which had 24/384 upsampling) and the original DACMagic (which did 24/192) as well the DACMagic+ which returned to 24/384 upsampling. The algorithm works very well and produces a very natural realistic sound which I felt was better than the typical BB SRC4192 typically used in DACs at the time.

Regards Anthony

"Beauty is Truth, Truth Beauty.." Keats

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