Noise in home audio recordings

[Markbnj]

Got a question for audio geeks. I'm into doing some home recording, nothing major, basically two channels for guitar and voice work. The setup I have is: 2 cheap dynamic mics (and I mean cheap, like $20), 2 decent XLR cables, an M-Audio DMP3 two-channel preamp, and the Realtek onboard sound chip in my Asus motherboard. I'm capturing the two channels on line-in and using Audacity for my DAW.

The problem is that the signal is noisy. I know I shouldn't expect much with this setup, but it's really noisy. If I record silence for a few seconds the result is like you grabbed a bit of the high-pitched part of a modem handshake and looped it. The noise is clearly visible in the captured waveform.

I disconnected the mics by unplugging the XLR cables and when I hit record I get a clean input line with no noise at all. The question is whether this means conclusively that the noise is coming from the cheap mics? I don't mind buying some better ones but I don't want to then find out that the noise is in the cables, or the mini-jack interface to line-in on the mobo I/O panel, or whatever.

Thoughts?

 

[JAG87]

Could be either. An easy way to test is to buy a cheap USB DAC with RCA inputs (like the UCA202). If your noise goes (mostly) away, then it's your mobo. If your noise stays, then it's time to invest in some better mics. I doubt it's the cables or the m-audio preamp.

 

[Markbnj]

Could be either. An easy way to test is to buy a cheap USB DAC with RCA inputs (like the UCA202). If your noise goes (mostly) away, then it's your mobo. If your noise stays, then it's time to invest in some better mics. I doubt it's the cables or the m-audio preamp.

Hmm, you've given me an idea. I actually have a Turtle Beach USB sound dongle that I use for my headset (for voip). I can use the mic channel input to test and see whether the noise is still present with these mics.

 

[JoeBleed]

not an audio guy, but you mentioned it sound like the high pitched tone of an old modem. Are you sure it isn't feed back from the mics being too close or too sensitive?

 

[Markbnj]

not an audio guy, but you mentioned it sound like the high pitched tone of an old modem. Are you sure it isn't feed back from the mics being too close or too sensitive?

Not 100% sure, no. They're cardioid and not directly overlapping, but it may be worth adjusting a bit. I'm somewhat limited in that I want to mic the vocals and the acoustic guitar.

 

[Howard]

Jumper the output to the input. That way you can send some real data to the input and see what happens. You won't be able to isolate just the input but the output is usually fairly clean on modern onboard audio.

 

[Markbnj]

Jumper the output to the input. That way you can send some real data to the input and see what happens. You won't be able to isolate just the input but the output is usually fairly clean on modern onboard audio.

That's an interesting idea. But I'd need line output, right? The headphone signal is amplified.

 

[nitromullet]

I see that the DMP3 has input level meters, so you can see your input levels. If you are getting a reading on these with your mic plugged in and not playing/singing it could be a noisy mic. If the input levels remain close to zero when you are not playing, chances are your preamp is introducing the noise.

 

[richaron]

I disconnected the mics by unplugging the XLR cables and when I hit record I get a clean input line with no noise at all. The question is whether this means conclusively that the noise is coming from the cheap mics? I don't mind buying some better ones but I don't want to then find out that the noise is in the cables, or the mini-jack interface to line-in on the mobo I/O panel, or whatever.

Yeah I would guess it's the mics from this... assuming gain is the same & it's set up ok. I would do more testing if you have appropriate cables, like:
-Line level into preamps with low/no gain.
-Line outputs from preamp into a stereo or speakers (careful of feedback).
-One of the mics into onboard 3.5mm mic input.
-And/or probably easiest, a different line level into onboard sound.

 

[Matt1970]

What is coming through your PC speakers? You do have some way to monitor the sound right?