Combine both stereo channels into mono?

Question

I combed the AudioManager and couldn't find any API or setting to switch from stereo to mono (both channels having a signal that's the sum of the two stereo channels).

Is it possible at all to accomplish this in Android?

Answer 1

There is a method in the AudioManager class called setParameters that might do that. Unfortunately, the API is not very clear about what it does:

public void setParameters (String keyValuePairs)

Sets a variable number of parameter values to audio hardware.

Parameters

keyValuePairs list of parameters key value pairs in the form: key1=value1;key2=value2;...

If we look at the source code for this method in AudioManager.java:

/**
 * Sets a variable number of parameter values to audio hardware.
 *
 * @param keyValuePairs list of parameters key value pairs in the form:
 *    key1=value1;key2=value2;...
 *
 */
public void setParameters(String keyValuePairs) {
    AudioSystem.setParameters(keyValuePairs);
}

And looking at AudioSystem.java:

/*
 * Sets a group generic audio configuration parameters. The use of these parameters
 * are platform dependant, see libaudio
 *
 * param keyValuePairs  list of parameters key value pairs in the form:
 *    key1=value1;key2=value2;...
 */
public static native int setParameters(String keyValuePairs);

Not much information there. It looks like the parameters might be hardware-specific, and I'm not even sure the parameters would do what you're looking to do.

Are you trying to set this system-wide or just in one app? I assumed system-wide, but if that's not the case, I'd imagine it would be easier.