Why is my input signal clipping?

Hi again guys,

I have a real tricky problem thats been bothering me for quite some time now.
When recording from mic source, I normally get clipping at the 0.5 level (ie half the max permitted level in the audacity track window) but I just cant figure out why.

First I suspected the rather crappy integrated “soundcard” line input on the motherboard. However, when I use the keyboard as sound source, there is no clipping at 0.5 level.
Mic goes through an old casette recorder equipped with mic inputs (yes I know this sounds rather crappy but it was a good recorder at the time) and outputs either on line output or on headphone output to line input of my pc. Im careful not to overload the mic input, at least according to the good led-indicator level meters on the recorder, have also used less than normal signal on the level meters, to no effect. There’s also a volyme control feeding both outputs of the casette deck.

I have old but good condenser mics, connected to an external phantom power unit and then to the casette deck.
At some point I got the impression that if I used the headphone output rather than line output, it solved the problem, but now I cannot reproduce that, and Im not sure any longer if it really made any difference.
Could there be an impedance problem between mics and preamp? Possibly, I would guess this preamp is geared towards dynamic (rather cheap) mics, while these are professional grade condenser mic with a rather strong signal (and incompatible imedance?)

Could it be a grounding problem? When I fiddle with the casette recorder I sometimes get small electric “shocks” when touching the metal case, so the voltage level on the case is probably not at ground level. The pc is connected to another power outlet than my stereo. So, could it possibly make any difference if I play around with turning around the AC-power connectors of the involved pieces.

Im sorry I cont describe this any better, If I tried with another preamp, it could perhaps give some answers, but for the time being I dont have one, and my budget doesnt allow buying preamps just for testing around and to isolate problems.

We have enough to go on.

You are overloading the microphone input of the sound card. There is a small, sensitive amplifier before the volume control on the sound card, so large signals will overload it (the 0.5 thing) and there isn’t anything you can do.

The Mic-In of the sound card is expecting a tiny, wispy, delicate mono sound signal from a microphone. The output of the tape machine is a large, powerful, Stereo signal. The two don’t cross well. If you have a deskside PC, change to the Line-In (blue?) instead of the Mic-In (pink?) and all your problems are over.

If you have a laptop PC, chances are you have no stereo Line-In and you have to buy one. These have been reviewed and seem to work well. People like the UCA 202.


Alternately, you can do as the system was designed and plug the microphone(s) directly into the sound card. Microphones produce a tiny, wispy, delicate mono signal, so the match should be very good.


I’m fairly sure you are overloading the input stage on the cassette recorder (which you are using as a pre-amp), and that its level indicator is further down the chain and seeing the (acceptable) output level of the clipped signal.

As Koz says, you are in the market for a new pre-amp. A USB pre-amp will also have the advantage that it bypasses the poor-quality sound card you say you have.


Hm, sounds fairly likely, so an usb-preamp is preferrable to and analogue feed to a (crappy) soundcard?
Do you have any suggestions on models? I was lookin at a esi
U46 xl
which looks quite ok, as long as you dont want to do stereo uptake of say an acoustic guitar
It looks like a jungle out there, trying to find a box doing the job without breaking the bank.

The advantage of a usb preamp is that it digitizes the signal so your soundcard does not have to. Notice that the device you linked to has 6 channel analog out. You’re looking for digital out. Analog in, digital out.

I’d have a look at this ARTcesories device USBPhonoPlus : http://www.artproaudio.com/products.asp?type=90&cat=13&id=128

I actually use the ART phono pre-amp - the DJPreII - connevted via my external USB soundcard (Edirol UA-1EX). If I hadn’t alreday got the Edirol I would stongly have considered the integrated ART device.