[Portaudio] ASIO unwanted loopback when channelCount = 1

Bryan Rambo bryanr at bometals.com
Tue Aug 1 09:27:41 EDT 2017

Please Note: this is not a bug fix request or bug report, just a friendly
Hi All,
Our application, OpenHPSDR/PowerSDR an open-source software defined radio
transceiver used by ham radio operators around the world, uses PortAudio to
pipe microphone audio into the application (for transmit) and pipe speaker
audio out of the application (for receive).
I am tracking an odd phenomenon when using the PA/ASIO api for a duplex
stream in which channelCount = 1 for both inputParameters and
outputParameters.  If the user's sound device is configured for two channel
(stereo) operation, then any audio being presented to the sound card's right
channel input is being looped-back to the sound card right channel output.
Is this the expected way for PA to handle channels on the host sound device
that aren't currently being used for the stream?
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