The number of channels expected to be pushed to the returned FPatchInput. If you need to downmix or upmix your input, try using the following: TArray MixdownGainsMap; Audio::FMixerDevice::Get2DChannelMap(false, NumInputChannels, NumOutputChannels, false, MixdownGainsMap); Audio::DownmixBuffer(NumInputChannels, NumOutputChannels, InputAudio, OutputAudio, MixdownGainsMap.GetData());