Route to specific channels of an ASIO Audio Interface

[Martin-S]

Dear FMOD-Team,

For an interactive art installation, I want to route 16+ discrete channels from Unreal to an ASIO audio interface using FMOD Studio.

I was able to route to specific programmer instruments in FMOD, but I’m struggling to route this events with programmer instruments to specific ASIO channels. Where can I set the channels?

I’m using a Behringer fca1616 interface right now, but want to use a bigger one later in the process.

My Versions:
Unreal Engine 5.5.4
FMOD Studio 2.03.07

Among other threads, I was reading How can I select specific output channels?, but for that I would have to use C++, right? FMOD Studio and Unreal Blueprints aren’t enough?

Maybe I’m missing something obvious.

Thanks so much,
Martin

[Connor_FMOD]

Hi Martin,

An option may be using a FMOD Studio | Effect Reference - Channel Mix. However, this will only support targeting 12 channels (7.1.4). If you wanted to be able to specify routing for more you will have to use code. We are always happy to help implementing the code for this!

[Martin-S]

Hi Connor,

Thanks a lot, the Channel Mix looks great. I tried the 7.1 aka 8 channel setup with my Behringer FCA1616. It works for some channels (FL, FR, C,…), but the signal of others (SL, SR,…) is also audible on other channels. E.g. audio routed to SL is also on FL but quieter.

Maybe I should go with specific routing and use code as you mentioned. Given that I’ll need more than 12 channels in the end. Can a programmable instrument handle this?

Thanks for everything!

Martin

BTW: I’m starting to like FMOD more and more, it’s really well designed

[Connor_FMOD]

Hi,

Great to hear you are enjoying FMOD!

@Martin-S

Can a programmable instrument handle this?

The programmer instrument wouldn’t handle any of the mixing. I updated our play_sound.cpp with a possible set up for how we could route audio to specific channels:

Example

#include "fmod.hpp"
#include "common.h"

int FMOD_Main()
{
    FMOD::System* system = nullptr;
    FMOD::Sound* sound1 = nullptr;
    FMOD_RESULT result;
    void* extradriverdata = nullptr;

    Common_Init(&extradriverdata);

    /*
        Create the FMOD system and configure it
    */
    result = FMOD::System_Create(&system);
    ERRCHECK(result);

    // Set up to use RAW output mode with 16 discrete output channels
    result = system->setSoftwareFormat(
        48000,                        // Sample rate
        FMOD_SPEAKERMODE_RAW,        // Disable speaker mapping for custom routing
        16                           // Number of output channels
    );
    ERRCHECK(result);

    // Initialize FMOD system with profiling DSP metering enabled
    result = system->init(32, FMOD_INIT_NORMAL | FMOD_INIT_PROFILE_METER_ALL, extradriverdata);
    ERRCHECK(result);

    result = system->createSound(Common_MediaPath("drumloop.wav"), FMOD_DEFAULT, nullptr, &sound1);
    ERRCHECK(result);

    /*
        Main loop
    */
    do
    {
        Common_Update();

        if (Common_BtnPress(BTN_ACTION1))
        {
            /*
                Set up DSP routing
            */
            // Create a ChannelMix DSP which allows explicit channel mapping
            FMOD::DSP* channelMixDSP = nullptr;
            result = system->createDSPByType(FMOD_DSP_TYPE_CHANNELMIX, &channelMixDSP);
            ERRCHECK(result);

            // Play the sound
            FMOD::Channel* channel = nullptr;
            result = system->playSound(sound1, nullptr, false, &channel);
            ERRCHECK(result);

            // Insert DSP at the head (pre-fader)
            result = channel->addDSP(FMOD_CHANNELCONTROL_DSP_HEAD, channelMixDSP);
            ERRCHECK(result);

            // Retrieve the DSPConnection for routing configuration
            FMOD::DSPConnection* connection = nullptr;
            result = channelMixDSP->getInput(0, nullptr, &connection);
            ERRCHECK(result);

            /*
                Set up mix matrix for routing
                Input: 1 channel (mono)
                Output: 16 channels
            */
            const int outchannels = 16;             // Total output channels (rows)
            const int inchannels = 1;               // Input signal channels (columns)
            const int inchannel_hop = inchannels;   // Step between columns per row (used for padding)

            float matrix[outchannels * inchannel_hop] = { 0 };  // Initialize matrix with silence

            // Route input channel 0 (mono) to output channel 1
            matrix[1 * inchannel_hop + 0] = 1.0f;

            // Apply the routing matrix
            result = connection->setMixMatrix(matrix, outchannels, inchannels, inchannel_hop);
            ERRCHECK(result);
        }

        result = system->update();
        ERRCHECK(result);

        Common_Sleep(50);
    } while (!Common_BtnPress(BTN_QUIT));

    /*
        Shutdown and clean up
    */
    result = sound1->release();
    ERRCHECK(result);
    result = system->close();
    ERRCHECK(result);
    result = system->release();
    ERRCHECK(result);

    Common_Close();

    return 0;
}

Using the Core Profiler (enabled by passing the FMOD_INIT_PROFILE_METER_ALL flag) we can see our mixing being applied:

This can be done in UE by expanding on the FMODAudioComponent class.

Will you be playing multiple instruments that will be routed to a specific output channel or an audio file/event will all the channels that need to routed?

I am happy to help setting up the custom FMODAudioComponent class.

Reference Docs:

• setSoftwareFormat()
• FMOD_INIT_PROFILE_METER_ALL
• DSP::getInput()
• DSPConnection::setMixMatrix()

Hope this helps!

[Martin-S]

Hi Connor,

Thanks a lot for your answer!

@Connor_FMOD

Will you be playing multiple instruments that will be routed to a specific output channel or …

Overall, I want to route from specific MetaSound Sources to specific ASIO Channels, ideally 32 channels:

@Connor_FMOD

I updated our play_sound.cpp …

Sorry for the newbie question: How can I integrate the play_sound.cpp? I guess I need to install the FMOD Engine. I never used C++ in Unreal or otherwise, but I have some experience with JS and C#.

Is there a tutorial about that? So far I have only used FMOD Studio and Unreal with Blueprints.

Thanks again,
Martin

[Connor_FMOD]

Hi,

Thank you for the information.

@Martin-S

How can I integrate the play_sound.cpp?

We wouldn’t be integration the play_sound, it was more an example of how it could be done.

@Martin-S

I guess I need to install the FMOD Engine

The FMOD Unreal integration has everything we need!

@Martin-S

Is there a tutorial about that?

Unfortunately not, but we can figure this out.

Something to mention is we have added support for playing UE meta sounds but that will add a layer of complexity to the issue. How are you using the meta sounds and would it be possible to use FMOD events instead? More information the better!

Thanks!

[Martin-S]

Hi Connor,

Thanks a lot!

@Connor_FMOD

The FMOD Unreal integration has everything we need!

@Connor_FMOD

Unfortunately not, but we can figure this out.

Wonderful, I can also be persistent if necessary.

@Connor_FMOD

Would it be possible to use FMOD events instead?

Unfortunately not, I’ll be using MetaSound very reactively, including the new Harmonix Plugin.

Thanks again for your help!

[Connor_FMOD]

No worries,

Would it be possible to share your UE Project? It can be uploaded to your profile. Or a stripped out version with some of your meta sounds?

Thanks!