Sample-accurate parameter automation

Matt · 29 November 2020 21:45

Hi,

Another question again:

I am building an effect that should accommodate quick parameter changes (think a wah pedal with a quickly-changing filter frequency).

VST3 supports sample-accurate parameter automation.

How do I correctly get to the parameters for each sample?

Do I just call GetParam() for each sample, or is there a better / more efficient way?

Obviously, I aim to absolutely minimise CPU usage.

Thanks,

Matt

olilarkin · 30 November 2020 11:43

I would first question if you really need sample accurate parameter changes since it will add complexity. Most plugins don’t need them. You’ll probably want some kind of smoothing on most parameters that you might want to automate precisely, and that somewhat negates the need for sample accurate

Do I just call GetParam() for each sample, or is there a better / more efficient way?

GetParam()->Value() just gets the value, it doesn’t tell you the sample offset, so you need to implement the OnParamChange() method and queue the param changes when sampleOffset > -1. In this example I’ve just queued them into a buffer, but there are better ways you could do that.

gist.github.com

https://gist.github.com/olilarkin/1a6e07a1d4ed6c9e20e81938fc1e1b2b

IPlugEffect.cpp

#include "IPlugEffect.h"
#include "IPlug_include_in_plug_src.h"
#include "IControls.h"

IPlugEffect::IPlugEffect(const InstanceInfo& info)
: Plugin(info, MakeConfig(kNumParams, kNumPresets))
{
  GetParam(kGain)->InitDouble("Gain", 0., 0., 100.0, 0.01, "%");
}

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IPlugEffect.h

#pragma once

#include "IPlug_include_in_plug_hdr.h"

/*
  This is a basic example of how to get sample accurate parameter changes in iPlug2 VST3 builds
 
  In reality you probably want to use some kind of queue such as those in the VST3 sdk... "public.sdk/source/vst/hosting/parameterchanges.h"
 
  Here we just write parameter changes into a buffer at their sample offset and output those values

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Matt · 2 December 2020 14:42

Many thanks once again Oli, I’ve got it working very satisfactorily.

Matt