Strange audio issue

**iamgnat** · 08-24-2005, 09:51 AM

Hi all,
This might be better off in the Audio forum, so run me off if appropriate

I am working on getting a Mac in my 04 Ford Escape (will be a mini, but i'm using my work supplied PB 800 as a test platform), and have run into a couple of issues trying to use it as the stereo.

I currently have an Alpine head with 3 Alpine amps (front, rear, and sub). I picked up a M-Audio Sonica USB adapter so I could run to my amps properly (by properly I mean have front-back & left-right fade support as well as timing control). The PB is an old 800 TiBook with USB 1.0.

The first issue is that at max volume on the Mac, the audio is not very loud (louder than "normal" people would like probably, but would be too quiet doing 70+ with the windows open). And on the flip side, when I bring the Mac's volume down below 25% I get no sound output.

The second issue is that on some songs, my right front speaker sounds blown (distorted/scratchy/etc..). When I hook my HU back up it is fine though.

I tried asking the shop that install the audio gear for me, and the rattled off something about home audio vs car audio using different power levels. It sounded good until I started reading these boards and don't see many others having sound issues.

Any one have any ideas what might be going on?

Thanks,
-dave

**Jirka Jirout** · 08-24-2005, 04:31 PM

It really appears to be a problem of signal levels. I am using a different USB audio adapter and it is not as bad as in your case, but the output from the computer is much more quiet than let's say a CD or radio on the same head unit volume setting (and Mac at maximum). Fortunately my head unit (old Sony CD XA 900) does have a signal level correction for the Aux input. I have to set it to +4dB to get the computer ouptut to the same loudness as the built-in tuner or CD.

Just to be sure - are you connecting the output of the USB adapter directly to the amplifiers or do you run it to head unit's AUX input?

**iamgnat** · 08-24-2005, 10:49 PM

Originally Posted by Jirka Jirout

Just to be sure - are you connecting the output of the USB adapter directly to the amplifiers or do you run it to head unit's AUX input?

Thanks for the info.

I am going straight to the Amps. I want to get rid of the HU (will move to my wife's truck so she can have iPod support there).

Thanks,
-dave

**simon_C** · 08-24-2005, 11:37 PM

have you tried running it directly from the computer? it might be your usb device thats causing the issue. and you could always get a preamplifier if necessary.

**iamgnat** · 08-25-2005, 07:15 PM

Originally Posted by simon_C

have you tried running it directly from the computer? it might be your usb device thats causing the issue. and you could always get a preamplifier if necessary.

Sorry it took so long to respond. I hadn't, but I did when I got home. I get the full range (i.e. I can hear music from 0% to 100% of the Mac volume), but at 100% it is still far below what my HU will do.

I played with the settings for my Sonica and got it to sound a bit better by adjusting the gain (I think it's the gain, it's not labeled and i'm a newbie to the audio stuff) to the max for the front/rear speakers and to about 75% for my sub.

Any other idea how I can work on this? Would adjusting the gain on my amps help?

Thanks,
-dave

**simon_C** · 08-25-2005, 07:29 PM

youre going to need to find a preamplifier (around 15-25w) to amplify the powerbook's headphone signal to match what the head unit was putting out.

see, what comes out of the powerbook, is very minimal power used to drive headphones (not even 1w) . what comes out of a car head unis is much more powerful (anywhere from 15-50w depending). so you see the issue? youre not feeding a strong enough signal into the amps.

**mbkowns** · 10-02-2005, 04:54 AM

Mine does the same thing he is describing except just my 300/4 amp does the low volume thing while my 500/1 sub amp doesn't. Also whats really wierd is it only doesn't sometimes.

I found that my opus psu was loose on the power plug and has been that way so I am think it might be my problem. I unplugged it and I am going to let it sit all night to see what happens. I will let you know tomorrow