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 sentence?

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 pulse.

The units of jitter measurement are picoseconds peak-to-peak (ps p-p), rms, and percent of the unit interval (UI).

See google.

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 the plugins.

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".

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