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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: One Comment, Two Questions posted by Gerry E. on February 9, 2009 at 09:40:12:
If you turn back the clock 20 years, Wadia and Theta were the undisputed leaders in digital audio, largely because they used custom filters implemented in Motorola DSP chips.
This started to crumble when the Levinson 30/31 came out. It was widely received as the best sounding digital product, yet used an off-the-shelf filter from NPC (later changed to the PMD-100 HDCD decoding filter).
With the rise of one-box players, people largely dropped the custom DSP-based filters. Now we are resurrecting them, as John Swenson notes in his post, with FPGAs. The learning curve is pretty steep with FPGAs. But we have been using them for years because that was the only way to do the things we needed to do with the video signals in our DVD players.
As far as "minimum-phase" filters, I think some people have played with them, but not in a big way for CD players. For example, there was a digital equalizer from Z-Systems that had minimum-phase filters. But most people implement minimum phase with an IIR. We found that an FIR sounds better, presumably because of the cumulative error as the data makes multiple passes through the filter of an IIR.
Using an FIR for a minimum-phase filter is so unusual that I couldn't find any software or equations that would let us do the de-emphasis with an FIR. So I did it the old-fashioned way -- with trial-and-error, converging on the target function.
And it doesn't matter what the competitors say. What matters is what the customers say. It's a nice story, but it only matters if it actually makes a sonic difference.
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Follow Ups
- RE: One Comment, Two Questions - Charles Hansen 19:18:08 02/09/09 (0)
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