mono AU fx?

is there any way to run an AU processor fx in mono? AU fx connnected to a mono input still output stereo. i have an elaborate electric guitar fx chain which could be more efficent in mono. tia! /dan


  • I think this is always going to depend on the plugin. If the plugin itself doesn't allow you to internally set it to mono, that's probably all you can do.

    Its possible some plugin acts differently based on a mono vs stereo input, but I wouldn't be surprised if all plugins take in stereo regardless. And it would be bad plugin design to do this because the AU host may not even support a mono input. Someone with better knowledge of AUv3 may have some more details.

  • Some plug-ins can crash hard when fed with one channel/mono. (AudioKit Rack Reverb is one that bails when fed with 1 channel).

    Most apps I've come across (even those being 'mono') still output a two channel stream (dual mono).

    Even AUM always works with 'two channels/stereo'.

    This can get annoying when recording a MONO input and the recording is always two channels even though it's 'dual mono' and wastes double the storage recording.

    One trick would be to add a 'mixer/stereo to mono' after the plug-in to keep it mono even though it'll likely be a 'dual mono' in the end when recorded...

  • on a pc, fx vst's like amp sims can detect if their input is mono & operate accordingly. is this not true for AUV3? i'm not sure we can tell in Drambo/AUM if an fx is outputing mono or stereo. they could just show a stereo output from a mono source. converting stereo output to mono doesn't avoid redundant processing.

  • In AUM the output is always two channel. If you feed it a mono signal it's most-likely converted to 'dual mono' before processing (this as the plug-in I KNOW crashes when using real mono-signal works sin AUM).

    The irony here is the AUv3's process what the host asks them to process and output what the host requests... in this case the 'host' would have to request mono processing from the plug-in and also request mono-output.

    So in the case of Drambo slapping in a Stereo to Mono (This will crashes AudioKit Rack Reverb as it can't handle mono signals which means only one channel is passed to the plug-in after Stereo to Mono) before the AUv3 and for 'safety measure' a Stereo to Mono to keep things mono in case the plug-in decides to output a stereo/dual mono signal.

    Keeping things 'mono' thru-out the signal chain is quite rare om iOS and I don't know a single host that does this properly and even real mono export/bounce seems to be a challenge (it always ends up being a dual mono and an audio-editor is needed to strip out the other channel).

    It is what it is...

  • guess i wish there were a mono version of the AU processor fx module. i'm always at the single-core cpu limit these days. seems a shame for logically mono fx like pedal & amp sims to work 2x as hard as necessary. @giku?

  • edited September 27

    in one word: no

    even if you feed them a mono signal

    they will output : dual mono or stereo

    if your mono signal hits a mixer stage with a pan somewhere along the way ... it will output dualmono anyway... because you listen on a stereo system output (your computer or audio interface)...

    (panned mono signal = stereo (left and right ch are not the same anymore)

    mono signal hard panned to mid = dual mono (both channels have the same signal)

    if you really need mono you can

    a) mix down the stereo channel to a mono ch or

    b) split the stereo ch and only use one side

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