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Old 12-01-2010, 04:04 AM   #1
variuse
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Join Date: Dec 2010
Posts: 1
Default [Max OS X 10.6.5] Robotic sound with USB audio after 20 minutes

Summary:
After connecting a USB audio device (e.g. Headset) on any Mac OS 10.6.x system, it works quite well for about 20 minutes. Then the voice turns into a noisy, "robotic" sound.

Steps to Reproduce:
- Connect USB headset / microphone
- Talk in Ventrilo for Mac for about 20-25 minutes.

Expected Results:
- Normal use without any issues

Actual Results:
- Noisy, robotic voice output after about 20 minutes

Workaround:
Manually disconnecting and reconnecting the USB headset solves the issue, but it reoccurs after 20 minutes.


This issue persists for a long time (since 10.5.x I think) and there're various threads about this in the forums.

Since it obviously seems to be a problem with Apple's USB driver implementation (AppleUSBAudio.kext) I originally created a bug report at Apple and I got some helpful information from their developer's team:

Quote:
Engineering has determined that this issue originates with a 3rd party. Please feel free to contact the 3rd party vendor (Ventrilo, Teamspeak or Skype as appropriate for your case) regarding this issue to help alert them of its importance.

Why it is not a common issue before Mac OS X 10.5.7
On Mac OS X 10.5.6 & prior, the USB audio driver publishes 2 audio engines, one for input stream and another for output stream. Applications could change sample rate on one audio stream without affecting the other stream. On 10.5.7 & onwards, a change in the USB audio driver publishes only 1 audio engine for both input & output streams. Changing sample rate on one stream will affect another stream (technically, the sample rate resides on the audio engine, so changing the sample rate naturally affects both streams). So in this case, changing the sample rate causes the input stream to run at a different rate that originally when Ventrilo launched. Ventrilo doesn't handle the sample rate change properly, resulting in the audio corruption (robotic/garbled, etc).

(a) This problem actually could occur on Mac OS X 10.5.6, depending on the USB audio device used. If the device can only support one sample rate, then this problem will also occur after the USB audio driver switches the sample rate on both streams when it detected one stream is falling behind.
(b) This problem is not specific to USB audio driver. Using Ventrilo for example with Firewire audio device also exhibits similar issue. The Firewire audio driver also puts input & output audio stream on the same audio engine.

In conclusion, this is a 3rd party application developer issue. Ventrilo (& other programs such as Mumble) need to listen to and handle sample rate change properly.
So maybe it's not the fault of AppleUSBAudio.kext driver implementation? Hope this helps to fix this annoying issue.

Regards,
variuse
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Old 12-01-2010, 04:05 PM   #2
Jaycyn
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Join Date: Mar 2009
Location: Florida
Posts: 313
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Without going in to too much detail, the email you received is inaccurate.

The audio issue persists in multiple applications, including their own apps. It has been documented and is a reproducible (sometimes) bug.

Unfortunately for the moment, nothing can be done to correct the issue. But stay tuned as more information will be forth-coming.
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