[MacOSX] 7.1 sound output on all channels

I am trying to create a player with FMOD-Engine using FMOD::System::playDSP. The System is configured for a 7.1 ChannelMap, for 7.1 SpeakerMode and 8 Speakers using setChannelFormat on the DSP.

But when I manipulate the buffer to send a stereo Signal to each port of the device (4 ports = 8 channels) I get a strange behavior.

The Front port (Front-Left & Front-Right) plays OK

The Back port (Back-Left & Back-Right) plays only the signal of its left channel

The Center / Bass port (Center & Lowfrequency) plays OK

The Surround port (Side-Left & Side-Right) plays nothing.

Also strange is, that if you set a MixLevelOutput on each channel with a value of 1.0f, the channel outputs and so the described behavior moves to a different port on the device like this:

Port Back output moves to port Center & Bass

Port Center & Bass output moves to port Surround

Port Surround output moves to Back.

I have already checked if the external USB Sound Device gets a signal on each of its channels via Audio Midi Setup on Mac. Also, I have tried to create Sound with pure CoreAudio API and this works also fine. I tried another software products that are not using FMOD and it also gives output to all output lines.

Is there anything else I could check?


Something worth checking is what Speaker Mode (FMOD API | Core API Reference) the Core System is currently set to using System:getSoftwareFormat().

Hope this helps!