Digital Audio Problems: Recording Play-Through; Muting the iSub

Continuing our coverage of digital audio input/output problems on a variety of Macs, we have reports on an inability to use play-through sound using a USB audio adapter; difficulty muting the iSub under Mac OS X 10.2.x;

Formac Play-Through A poster in the MacFixIt forums laments over the Power Mac G4's inability to play-through sound that is being recorded through a n expansion audio card, such as Formac's ProTVStereo.

The lack of a standard analog 'audio-in' port on the latest Power Mac G4 desktops necessitates an external USB audio adapter, and playing recorded sound through the Mac's speakers has turned out to be a challenge:

"Owing to the design of the motherboard and the absence of an analog 'audio-in' port in back of the G4's tower, I've had to buy an Edirol UA-1A USB audio device in order to import sound into the Mac while recording video on a Formac ProTVStereo. And it works. Using RCA plugs:audio 'Out' and 'Into' the Edirol device, which then connects to a USB port in back of the tower.

"Inside the ProTV's window panel, you select "USB audio device" and now you can get in-sync audio/video. The problem is, you don't get play-through sound. You can't 'hear' what you're recording while you're recording it. And you can't adjust the input volume."

"The Edirol device does have audio 'Out,' using RCA plugs, which allows you to hear sound output. However to take advantage of this you need the following: a pair of external speakers able to accept a 1/8 audio jack ( But not connected to the Mac's headphone port otherwise you hear nothing ) and special cable: RCA plug on one end, 1/8" audio jack on the other. But this produces a kind of feedback 'echo' which is really annoying ( on play-through only, the actual recording itself will be OK when you watch it. )

"The G4 has a special speaker port which works in conjunction with the sound control panel to adjust volume, etc. But it only works with Apple Pro Speakers, and you can't plug anything into those ( like the Edirol. ) Unless you wouldn't need to, and Pro speakers let you hear play-through sound? So I'm at a loss as to how to get around these obstacles? How can I hear clear audio and adjust the input volume while I'm recording?"

Muting the iSub Jonathan Chase reports problems muting his Harman Multimeda-designed iSub subwoofer:

"I upgraded to Mac OS X 10.2 a week or two ago and just noticed that if I'm playing music (from iTunes) and hit the keyboard mute button, the sound continues to play (although in a muted, bass-heavy fashion) through only my Harmon Kardon iSub. I'm running a flat panel iMac 800 MHz SuperDrive (15" monitor)."

UPDATE: Apple Knowledge Base article #107057states that in order to completely mute the iSub, volume to the device must be turned off from the Sound pane of System Preferences:

1. "Choose System Preferences from the Apple menu.
2. Choose Sound from the View menu
3. Click the Output tab.
4. Select the checkbox for Mute next to the iSub volume slider."

Feedback or workaround possibilities for this issue? E-mail late-breakers@macfixit.com

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