Sound becomes muffled after several seconds of recording

[Phantai]

Hi all!

I'm a film maker by nature, but decided to record some music. Sadly, the only microphone I have is a shotgun microphone specifically for filming. Thankfully, it produces a very nice and crisp sound, and with the right preamps, I can get a decent recording of vocals or even instruments.

However, i'm having a problem with my recording software (or maybe it's with the mic?). All of my recordings start out very crisp and clear, and then 3 or 4 seconds in, become fairly muted and muffled. I'm not sure why this is. When I use this microphone for filming, the sound is crisp the whole way through.

It may have somethin to do with automatic preamp settings. Is there anyway to manually set the preamps with programs like audacity?

 

[kubeek]

Preamp usually is separate device, and not controlled by programs. What soundcard/interface do you use?

 

[SouthSIDE Glen]

I second kubeek's request: could you describe your signal chain from microphone to computer - including mic preamp, computer interface and software?

G.

 

[Phantai]

I second kubeek's request: could you describe your signal chain from microphone to computer - including mic preamp, computer interface and software?

G.

Aren't the preamps regulated by the software though? (Sorry, complete sound n00b!)

I have my microphone plugged into an XLR to Mini adapter, which is plugged into my laptop. The laptop is a Compaq. the software is Audacity (but I've tried it with Sony Vegas as well, same results).

 

[mjbphotos]

Then you don't have a pre-amp (which is a separate outboard device) You need a preamp to boost the signal up to an acceptable level. Not sure why you are getting acceptable volume to start, though.

 

[SouthSIDE Glen]

Aren't the preamps regulated by the software though? (Sorry, complete sound n00b!)

I have my microphone plugged into an XLR to Mini adapter, which is plugged into my laptop. The laptop is a Compaq. the software is Audacity (but I've tried it with Sony Vegas as well, same results).

On an integrated computer sound card like yours, yeah the pre is controlled by software.

At least part of your problem, though, Phantai, is that you really should not be using that preamp device for your music recording. Not only are laptop soundcards notorious for their poor-quality peamps in general, but the mic pres on integrated computer sound cards are really designed for gaming and Internet chat-style microphones like headset mics and conference camera mics, which generally are spec'd at different output and impedance levels then the better-quality mics meant for prosumer music and video use (what kind of shotgun are you using? Sony? AT? Rode? Other?)

I'm not positive what's causing your specific symptom, It's a strange one I've not encountered before, but I do have an edumacated guess (though just a guess). I think maybe the soundcard may be injecting some very low frequency (0.3Hz or so) offset into your signal that winds up strangling your headroom on the high-frequency peaks.

One way to attack that would be to look up "DC Offset" in Audacity's help file to find where it's DC offset switch is located. This switch toggles a very low frequency filter that will eliminate that problem if that is the cause.

But if you really want to do it the "right" way, you can get an entry level preamp/interface box that will accept your XLR connection straight and is designed to work properly with that kind of microphone. This box will output via USB or Firewire (depending on the model, but typically it'll be USB) direct to your computer, bypassing the cheapo soundcard in the computer altogether, and recording direct to the software of your choice. You can get acceptable one-channel preamps/interfaces for around $79 new, and 2-channel interfaces for $149 new.

G.

 

[Phantai]

Thank you! That was a very informative post. I'll try the Audacity thing you mentioned, and I'll report back with the results.

If it matters, I'm using an AT shotgun.

There was a preamp box I was thinking of getting for my filming (seeing as my camera has subpar preamps). It's called a Beachtek Adaptor, and it was designed for filming. It has two balanced XLR inputs, and all the controls you would get for a decent preamp. The box does everything itself, and can convert the signal for an unbalanced mic jack (So I can plug it into the PC if I wanted). Would this suffice for recording to my PC? I'd just like to kill two birds with one stone

 

[SouthSIDE Glen]

If it matters, I'm using an AT shotgun.

Good man!
(I like the ATs for video/location shooting also.)

There was a preamp box I was thinking of getting for my filming (seeing as my camera has subpar preamps). It's called a Beachtek Adaptor, and it was designed for filming. It has two balanced XLR inputs, and all the controls you would get for a decent preamp. The box does everything itself, and can convert the signal for an unbalanced mic jack (So I can plug it into the PC if I wanted). Would this suffice for recording to my PC? I'd just like to kill two birds with one stone

I'm not familiar with that specific device, but it sounds as though it would work - though there are important caveats there as well. It probably outputs audio line level and not mic level (that is, after all, what the preamp is supposed to be for ). You'd want to check if it outputs a "pro" line level of +4dBu or a "consumer" line level of -10dBV. If it's pro line level , then you'll still have a bit of a level mismatch with the consumer sound card's line level spec. This is not killer problem, but it's far from ideal, especially if you're going to be spending money on the external preamp - you might as well get it right.

You really are best off avoiding that soundcard altogether if you can help it. Laptop soundcards are *notorious* for their slipshod quality, usually noticably far worse than even normal desktop PC soundcards, which while servicable, are not that great either. They are made for games and for playing movies through computer speakers, not really for audio recording with any kind of real fidelity.

I'd recommend looking at something like a Tascam US122L, which is a small, portable box that accepts up to two channels of either line, instrument or mic input, with decent-sounding preamps for the price range, and also has it's own digital converters that go straight to USB digital output, which you can plug directly into your laptop's USB bus, bypassing that soundcard altogether.

G.