What is the CPU usage issue with Delay2?
Consider the structure below, with the settings we have on the controls, there could potentially be a very long “tail” on the echo with such a feedback level. Ok so it reaches a low level, but it could take a very long time to reach what SynthEdit considers “silence”. Why does this matter?
Well any modules further downstream are not getting shut down as they should be, and could still be active long after the human ear would fail to detect sound from the echo. This is a waste of CPU, as these modules are relying on SE telling them that they are not receiving audio, meaning they may not go into “sleep” mode for a long time. There is no risk of generating “Denormal” numbers as SE removes these internally.
Here is a quote from a regular contributor on the SE group Andrew Ainsley:
“I sleep my modules when it is approximately under -110dBFS(noise floor of the best high-end AD converters, and humanly detectable dynamic range is approximately 120dB), and I’m assuming Delay2 sleeps at somewhere just before denormal mode, which is very very low, I tested up until -250dB and Delay2 is still active for quite some time afterwards…In practice say, with a max delay of 1 sec and 50% feedback, Delay2 will take in the order of minutes to go to sleep, which in practice is longer than a typical song, which seems rather pessimistic to me – i.e. in practice it will never sleep even though it can sleep, and thus it also keeps downstream modules awake while processing an inaudible signal. Switching it off sooner (in level) might cause audible clicks, but even if you assume the end-user will boost the level by an unrealistic value of say +120dB(!), you should still be safely able to switch off at about -230dBFS. “
If we look at the chart below you can see what is meant by the tail, the red section is where the reverb/echo is tailing off (The purple section). At high feedback levels this tail can potentially become very long if there is no cut off point set other than 0, even though we can’t hear the sound. We want to keep the green and blue sections, but it would be very handy to be able to remove the inaudible section of the tail.
How can we stop this waste of CPU?
Fortunately Jeff has introduced a new module in SynthEdit to prevent this issue-the Silence Gate. This module does not wait for complete silence (0), but shuts off the audio at a level where we can’t actually perceive the sound. (Jeff has not quoted a level for this, just that it is completely inaudible.
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