These would be handy
void applyGainRamp (
int startSample,
int numSamples,
float startGain,
float endGain) noexcept;
void AudioSampleBuffer::addFrom (
int numChannels,
int destStartChannel,
int destStartSample,
const AudioSampleBuffer& source,
int sourceStartChannel,
int sourceStartSample,
int numSamples,
float gainToApplyToSource = 1.0f) noexcept;
etc…