[sdiy] CD sound quality evolution

Brian Willoughby brianw at audiobanshee.com
Tue Feb 16 03:25:50 CET 2021


On Feb 15, 2021, at 14:40, Mike Bryant wrote:
> No they weren't.  I don't know which year you are referring to but early BB DACs were at best 14 bits, maybe 15 for good ones.  And they sounded dreadful - almost everyone working in pro-audio agreed.

I cannot find reference to any Burr Brown DAC chip that's less than 16-bit.

Are you saying that they were only accurate to 2 LSB, and thus were effectively 14-bit despite accepting 16 data bits? There were certainly many different price points, depending upon accuracy, and all of the audiophile ones that I heard about were much more expensive.

My direct experience with BB DAC chips started in 1988, so that would be the time frame. I cannot find the exact part number that was used in my NeXTdimension and NeXTstation computers, but the sound quality was phenomenal.

I'm talking about the PCM58 (1988), PCM63 (1990), PCM64, PCM65, PCM1701. Some of those were a decade later, though. Burr-Brown pioneered techniques like active laser trimming, which I witnessed at their competitor, Analog Devices. This was all before delta-sigma became common, although Southworth had a 24-bit delta sigma audio card for the Macintosh II computer perhaps as early as 1987 before they went out of business.


>  The Sony 1 bit DACs released in 1987 quickly replaced them in most digital audio installations.
> 
> In 1983 we had already demonstrated near 20 bit performance at 80kHz sampling at HP.  It wasn't commercially viable at the time as it couldn't be integrated into a single IC, but it showed it was possible if Philips and Sony had just waited a little.  Our work was based on a Philips paper anyway so I suspect their engineers also had a 20 bit system working, but marketing probably pushed to get it out of the door before it's time.  The other problem was the lasers weren't good enough to get 45 minutes of 20 bit data at the time so we would have had to wait for those as well.

I frequently get the impression that Sony did not try to make the *best* digital audio system, but merely an affordable one that was good enough. After they settled on a workable design, via committee, they set about to hype it well beyond its actual capabilities while simultaneously underplaying the potential advantages of analog recording.


> Totally agree on your later comments.  A lot of the work was done on dithering by lots of people, not just in the audio field.  In fact audio tends to follow other fields, not lead.  The headroom issue is when you only have 16 bits.  But even most CDs now are over-compressed to my liking.  SuperCD solved that problem but never took off.

Meanwhile, PCM releases are being made that are not over-compressed. See HDtracks - although it's basically impossible to glean the provenance of their media without buying it first. Warp Records has artists like Squarepusher who do not over-compress their releases, which are available in 24-bit via Bleep.com


> The Phil Collins problem was infamous at the time, but is long before the Internet.  It was caused a particular pattern confusing the error correction on some but not all CD players.  They recalled them all and replaced with a new mastering that removed the problem sequence.  And of course record companies then realised they had to test CDs are more than one machine, a new experience for them of course.

That sounds like the EFM (eight-to-fourteen modulation) or some other very low level aspect well ahead of the audio samples was in effect. Are you talking about the lossless CIRC error correction, or the lossy sample interpolation that takes place only after error correction fails?

Brian





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