The "say" command in OSX Terminal works fine for me and I use it now end then. However, since last week it produces the following error message on my Mac Mini (Late 2012, 10.8.4):

$ say test
> MTBEAudioUnitSoundOutput::PropagateProperty Error -10851
> MTBEAudioUnitSoundOutput::PropagateProperty Error -10851

The sound is produced as expected, so no big drama, but I'd like to know if somebody else suffers from the same problem or if that error has something to do with my specific setup here... and, of course, what this message means.

3 Answers 3


A little Googling suggests that it's a new problem in 10.8.4. A couple people in this MacRumors forum thread have experienced the same, as has the author of this blog post. No indications as to how to get rid of it however.

I haven't seen any error when testing say, so it may be some combination of hardware that causes it, but if the sound output is as expected, I wouldn't worry too much about it, and it will probably be fixed eventually.

If you're using say in shell scripts and need the Terminal output cleaned up a bit, you could always pipe it through grep: say test | grep -v "MTBEAudioUnitSoundOutput::PropagateProperty Error -10851".


I'm just piping stderr to /dev/null for now, i.e.:

say test 2>/dev/null
  • 3
    This suppresses the error message, but doesn't really solve the issue...
    – nohillside
    Jul 7, 2013 at 6:47
  • 1
    Well, if the sound outputs as desired then what problem is there besides the undesired error message? So if it makes the error message go away, the problem is solved, unless we discover more side effects.
    – Daniel
    Sep 17, 2013 at 15:59

The error number is a constant named kAudioUnitErr_InvalidPropertyValue

It also shows up when using the NSSpeechSynthesizer API with the new voices in Mountain Lion.

NSString *string = @"Hello World";
NSSpeechSynthesizer *synth = [[NSSpeechSynthesizer alloc] initWithVoice:nil];
[synth startSpeakingString:string];

reference: https://developer.apple.com/library/mac/documentation/AudioUnit/Reference/AUComponentServicesReference/Reference/reference.html#//apple_ref/doc/uid/TP40007291-CH7-SW1

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