Performance Meters

This dialog provides an overview of the computer’s audio processing performance.

It is sometimes the case that a very fast computer displays low CPU usage; and yet it occasionally is delayed (or: “interrupted”) so that it cannot meet the deadline imposed by the audio system’s input/output buffers. The Performance Meters dialog is intended to help troubleshoot this problem.

The reports include:

• Buffer size: this is the user’s selection for bufferize and the resulting milliseconds of latency incurred by the buffer
• Idle: this reports on the percentage of time spent idling between each soundcard buffer
• DSP: this reports on the percentage of time spent in DSP processing for the soundcard buffer
• Engine: a sub-category of DSP, this reports how much time the audio engine (soundcard I/O and resampling) is using
• Session: a sub-category of DSP, this reports how much time the session (channel processing, plugins, bussing, etc) is using.

Desktop computers are not intended to be “woken up” at the audio rate of 44, 48, or 96k times per second. So in a computer’s digital audio system, the audio data is buffered (accumulated) in the soundcard before being offered to the operating system for processing. When a soundcard’s “recording” buffer is offered to the computer’s CPU, Mixbus has an opportunity to process the audio buffer and then return it to the soundcard before the soundcard needs to “play” it out again. At a buffersize of 1024 samples, and 48kHz, this means that Mixbus must ‘wake up’ every 21 milliseconds, process the audio, and return it to the soundcard before the deadline is met.

The “Performance Meters” dialog collects this data and reports it to the user. The values captured are the worst case for any buffer that the computer has received. So the value won’t exactly match the instantaneous DSP% reported in the top of the main window. This “worst case” data is used to determine the realtime stability and performance of a computer.

The “Idle” and “DSP” numbers will always combine to match the available buffersize/latency.

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