Software jitter

Paul McGowan writes:

Just when we thought we had it all figured out along comes a new form of distortion to tackle: software jitter.  The culprit here is, unfortunately, a very necessary component in the chain of digital audio – the CPU (central processing unit) itself.

We first noticed this problem when we started releasing different versions of software and firmware – every release of our music management program eLyric sounds different and every release of the Bridge firmware sounds different.  This might seem obvious to you but not to our designers since the changes we were making had “nothing” to do with the data stream or the audio itself.  Sometimes a change in the front panel display code would cause a major upset in sound quality.

Turns out the core of this issue is our old “pal” the power supply – the problem we started working on in 1975 when we introduced external high-current power supply options and again in 1997 with the Power Plant.  Differences in code change how the CPU chugs along or gets wild with activity – which in turn modulates the power supply causing tiny voltage shifts.  These voltage shifts affect the transition area between a 1 and a 0 causing a temporal shift in the data called jitter.

Of course it should be obvious the way to fix this isn’t in the code that causes the changing flurry of CPU activity but in the hardware itself – a much bigger challenge.  You can see some of this work reflected in our new MKII upgrade of the PWD where we went from a couple of localized regulators to 11 – all in an effort to minimize the effects of software jitter.

I wanted to write this post to keep you up to date with what’s being discovered in our industry.  Look for changes in hardware and lots of controversy surrounding this finding.  I am sure it’ll rise to the top shortly.

Leave a Reply