On Sunday, 29 November 2015 at 09:12:18 UTC, Any wrote:
On Sunday, 29 November 2015 at 06:18:13 UTC, Jonny wrote:
um, come on, you sit here and preach that I don't know what
I'm talking about yet you can't even be right on the first
jitter is the standard deviation of the timings. Do you know
what standard deviation is? It is the square root of the sum
of the squares...
Jitter is any deviation in, or displacement of, the signal
pulses in a high-frequency digital signal. The deviation can be
in terms of amplitude, phase timing or the width of the signal
The units of jitter measurement are picoseconds peak-to-peak
(ps p-p), rms, and percent of the unit interval (UI).
We're talking about whether a plugin / audio code / runtime
environment can deliver audio to a soundcard in a reliable manner
so that you don't get audio drop outs. We're not talking about
the jitter of a digital clock source that's used to control the
actual sampling stream. It's similar but at the level of the
audio buffer timeslice, not the unit delta of the sample stream.
The jitter of an audio clock source is for electronic engineers
not audio plugin developers.
In general terms of delivering audio to a soundcard jitter would
be the variation in the time take to deliver each buffers worth
of audio data to the soundcard. If the sound card has 5ms
latency, then you need to make sure your audio processing never
takes more than that.
The point is that it is better to have an algorithm that always
takes 3ms, than one that usually takes 2ms but occasionally takes
6ms. Because those times when it takes 6ms it cant feed the
soundcard in time for the next audio buffer to be delivered.
In more precise terms jitter is the variation in the time a given
algorithm takes to process. I mean if the code is identical and
doesn't change from one buffer to the next, the variation in time
take to produce a each buffers worth of data.
It's important to remember that a typical DAW user may have 10,
20, or 100+ plugins loaded, and it may be hitting 80 or 90
percent CPU usage in places. With constantly changing loads on
IE. If you are at 90% cpu usage with 5ms timeslice you can only
tollerate 0.5ms jitter before the shit hits the fan. So the
important question is not "does it work", it's "does it work
under heavy load".