hiss upon playback

[scocious]

I sang and played guitar into a mike (no Phantom Power requirement), from there into an M-Audio Mobile Pre USB (audio interface), from there into my computer (Audacity 1.2.4). A couple of songs were on single tracks, and one was multi. Things have always worked out well before. The recordings were generally OK except that they were spoiled by an awful background hiss, whether played from the hard drive (via iTunes) or on my stereo on a CD burned from the hard drive. Any possibilities?

[steve]

When you have recorded into Audacity, do you get a good strong signal or do you have to amplify it a lot? If the signal into Audacity is low, then you will need to turn up the gain on the pre-amp.

[scocious]

Thanks,
The input level meter seemed OK - about halfway and no clipping. The pre-amp gain for the line in was turned to the max.(I've never gotten clipping with just an acoustic instrument.) Still, I've never been all that pleased with the volume I end up getting on playback. Don't know how relevant this may be, but nothing else was unusual: 32 bit float, 44,100Hz, mono track. So I don't know what might have caused this hissing.

[steve]

Pre-amps often have a sudden increase in noise when they are turned up to Max. Guitar outputs are typically a fair bit lower than line level so really the signal should be amplified a bit before it is fed into a line level input. If you don't have the equipment to do this, try turning down the gain on the M-Audio just a little bit. The signal level will be lower, but you may find that it is significantly cleaner. Can you turn up the volume on the guitar?

[scocious]

I'll see what happens with the gain on the M-Audio turned down some. It's possible I didn't have it at its max in the past. (And since I'd never had clipping issues, I was hoping to get a bit more volume to the end product.) The guitar is acoustic. I have it's sound and my voice both going into a mike, which I plug into the M-Audio line in. So there's no other control on guitar volume excepting how loud I play. I suppose I could use a pickup and plug that directly into the 2nd line in, using the 1st line in for voice only via the mike. I always figured the recorded sound I'd get that way wouldn't be as faithful to the live acoustic guitar sound. Thanks again.

[steve]

I have it's sound and my voice both going into a mike, which I plug into the M-Audio line in.

If you are really plugged into the "Line in" socket, then that will account for the problem. You should be plugged into a microphone socket. If you do not have a microphone lead with an XLR plug (to fit the big 3 pin socket) you should get one. The 3 pin microphone socket will give you much more signal with the gain turned up far less. I would expect it to make a considerable difference. If your microphone does not have a detachable lead, then get a better microphone - it'll improve the recording quality a lot. (a large diaphragm condenser microphone would be ideal for an ambient recording of acoustic guitar and vocals (something like this http://www.samsontech.com/products/prod ... &brandID=2 ). I would stick with a non-USB microphone so that you can take full advantage of your current equipment.

[scocious]

Wow.....Thanks once again. We'll, I'll get the equipment and try that too. Plus maybe I'd be better off in terms of quality by miking voice and guitar separately - i.e. 2 mikes. I still can't figure out why I had no hissing issues in the past, but maybe it just was a matter of having the gain at its max.

[scocious]

One last thing......That mike you referenced needs phantom power. If I wanted to go to two mikes, I'd guess that the no-phantom power Shure PG58 I have couldn't be used along with the new one (since I'd have to press the phantom power button on the pre-amp)?

[steve]

If I wanted to go to two mikes, I'd guess that the no-phantom power Shure PG58 I have couldn't be used along with the new one (since I'd have to press the phantom power button on the pre-amp)?

"Shure PG58" - not exactly a classic recording microphone, but not terrible either. You would certainly get better high frequency response from a studio condenser microphone (a more natural ambiance and greater detail), but simply using an XLR lead to connect the Shure to the microphone socket should provide reasonably good results.

Ideally you should not use phantom power with a dynamic microphone, but it is unlikely to cause a problem if you do. The microphones where you MUST NOT use phantom power are "ribbon microphones" and some "electret microphones". Using phantom power on electret microphones may (depending on the microphone) stop the microphone from working or cause excessive noise, though some electret microphones are designed to use phantom power. It is unlikely to cause permanent damage, but it would be wise to check the instructions before attempting to connect an electret microphone to phantom power. Ribbon microphones on the other hand will usually be destroyed by phantom power.

Dynamic microphones are largely unaffected, though they may pull down the phantom power voltage a bit and thus the possibility of reducing the performance of a condenser microphone that is being powered from the same supply. It is unlikely to cause a problem, but a bit of careful testing would be worthwhile.