PS Audio: Having your cake

Paul McGowan writes:

For those of you following the trail of the Music Room construction and the installation of the Infinity Reference Standard loudspeakers, the latest chapter, part 6 is up and ready for viewing.  Part 7 will probably follow quickly as the IRS system is, as of this morning, setup in the room!

Yesterday’s post stirred some controversy and prompts me to both apologize and explain a little further.  I said that neither analog nor digital are continuous process and the apology comes because that happens to be more of a philosophical point of view from my part – as I look at the entire universe as an illusion of whole – but sharing my personal viewpoint on such things isn’t appropriate for this column.  Sorry.

Maybe a better way to put it is like this: if you consider analog continuous, then so too is digital. This is because within the bandwidth of the system’s agreed upon end points nothing ever stops – it is in fact continuous – certainly if we look at the output.

You can’t suggest that one is constantly moving while the other stops and starts if within the same limitations we see no discontinuity.

I think people get confused with this and get the idea that an analog system is doing something the digital system is not between the digital samples – in other words, if you’re imagining the digital system as starting and stopping to do its job and the analog system as continuous – then you believe the analog system is continuing to work between the tiny gaps of the digital system – and that’s not true.

If the analog system were, in fact, doing something between the digital gaps, then the analog system would have a much higher frequency response than it does, since we can all agree that those digital gaps are at a specific rate that we can calculate – and that rate is outside the bandwidth of the system.

Modern digital audio systems run at very high rates of speed.  Take our upcoming A/D converter we’ve been touching on.  That device runs at 6mHz – 6 million times a second.  Indeed, it is stopping and starting 6 million times a second – but you know that not from its results – only intellectually.

When the first digital audio systems hit the street they were running relatively slowly compared to today.  Those first systems struggled to deal with 20kHz – such that there had to be an incredibly steep filter in front of the ADC and at the output of the DAC – so steep (extreme) that at 22kHz there had to be essentially zero input or output.  Let me tell you, the kind of filter that gives you 100% signal at 20kHz and zero at 22kHz has a major impact on sound quality.  It was one of the reasons digital sounded so awful and even today many of the older CD’s were mastered using this brick wall filter.

Today’s ADC’s and DAC’s run so much faster and operate so differently that this filter has become almost trivial.  Our new ADC, for example, has a single gentle rolloff starting at 50kHz and it just takes its time getting low enough to not matter to the DSD converter running at 6 million times a second.

So you can’t put one system under a microscope and say “aha! It is stopping and starting and really not continuous – therefore we must be missing something when compared to our cherished continuous system that is capturing everything”.  That would be like having your cake and eating it.

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