Error 501 Audio mix batch failed to apply

I used Cantabile for more than a year without any problem.
Recently I changed my master keyboard and now i’m using a Kawai MP7 connected via USB. Everything else is unchanged (Pc, audio interface, plugins)
From then, when I start Cantabile 50% of times I get no sound and all the lights in Cantabile are dark, like if it doesnt receive any midi data
If I go in Tools-> Settings and simply press ok without changing any settings, it works…
Initially I thinked there was I problem with the midi Kawai driver (because the only thing I changed in my setup was the keyboard), but then I found this error message in the log file
Audio mix batch failed to apply
With error codes 501 or 502
Any idea ?

Hi @Andre68

That error message about audio mix failing to apply is generally benign but might indicate and issue with the audio engine (or audio driver, or a plugin) stalling for an unexpectedly long time.

So I think it’s a side effect of the problem - not the cause of it.

It sounds to me like an issue with driver failing to start, or taking a long time to start. Can you send me a debug log:

  1. Start Cantabile and make the problem happen.
  2. Restart the audio engine to clear the problem (instead of going to options just power cycle with the button top right of Cantabile’s main window)
  3. From the Tools menu, choose Open Settings Folder
  4. Close Cantabile.

From the folder opened in step 3, send me the files log.txt, log-previous.txt and settings.json and I’ll take a look.


Thanks @brad, I collected the log files but the forum says that I cannot upload them because I’m a new user. There is another way to send them to you ?
Thank you!

Hi @Andre68,

Yep you can email them to me -


Hi @Andre68

I’ve had a look at the logs and there’s definitely something blocking the audio engine. This is apparent in a few spots including the aforementioned audio mix batch failures but also other operations taking a long time (eg: stopping the recorder service taking > 5 seconds).

If this problem disappears when your Kawai isn’t connect then yes I’d be very suspicious of any drivers related to that device. Unfortunately, to know for sure I’d probably need to add more logging. Have you checked for new drivers from Kawai (or perhaps try older ones if you can get them).

btw: I also noticed this in your log file:

00003040        0   [00336:2]:       CoreEngine - Processor concurrency reported as 4
00003040        0   [00336:2]:       CoreEngine - Thread pool size set to 8
00003040        0 ! [00336:1]:       CoreEngine - Excessive threads specified for parallel execution pool

Unless you have a reason for otherwise, I recommend settings the number of audio threads back to 4 (in Options -> Audio Engine).