Frequency problem in recorded voice samples

[kijciwoko]

Hi!

I'm currently working on a voice telediagnostics system which uses voice samples (44100 Hz, 16 bit, mono) to detect voice parameters. To record samples I'm using Audacity v1.2.6. And here's a thing:

When I'm recording samples on my laptop (windows 7, realtek hd audio and mic "inside" the laptop (don't know what's the professional term in English)) it works fine - analysis give good results (as it did before, when I used Win XP windows recorder) and my voices base frequency is about 124 Hz, which means it's perfectly fine. But when I'm trying to plug-in any kind of microphone (I've tried 6 different types) on any computer (tried on 3 other laptops and one standard PC, all different sound cards and OS), it tells me that base frequency of my voice is somewhere between 2 and 4 kHz which is simply stupid. I've check 92 samples recorded on different configurations and the problem is common. The only constant thing was the Audacity program. What can be the cause of my problem? Are there some secret settings which prevent recording voice samples on plug-in microphones?

Here's how it looks (apparently it's not only frequency problem but amplitude too) - top is the correct sample recorded on an "inside" mic, bottom was recorded on plug-in Manhattan Gooseneck microphone:


Thanks for your help,
Adam.

[steve]

Could you post two short examples as WAV files (see the "Upload Attachment" tab below the message compose box).
The samples only need to be a couple of seconds long - the examples below would be ideal.

Audacity is often not able to control the sound card volume settings on Vista, so you need to set the record level manually via the sound card control panel. One way you can get to that is through the Windows Control Panel http://wiki.audacityteam.org/wiki/Mixer ... trol_Panel

Vista and Windows 7 often have "Advanced enhancements" for the microphone input which are designed to make poor quality sound cards sound more reasonable for Skype and other such applications. Unfortunately they also tend to make a total mess of recordings, so they should be switched off. Look in the Windows Control Panel, find the microphone input and check for any advanced effects. The microphone input should normally be set for "44100Hz CD quality mono".

By the way, Audacity 1.2.6 is not recommended for Vista (Audacity 1.2.6 is ancient). The recommended version is currently Audacity 1.3.12 http://audacityteam.org/download/

[kijciwoko]

Thanks for answer. The problem is, in advanced properties of the microphone there's no format which I'm using. The closest one is 2-channels (need mono), 16-bit, 44100 Hz, but there's also option "allow applications to take control over that device" (and it's on). Do I need new sound card driver? Microphone volume is set to 100% and the microphone boost is off.

I'm not an expert, but is it possible, that for some reason there are 2 microphones in my laptop (sony vaio) and that's why it records properly (cause of the 2-channel setting) and after plug-in a mic it tries to record stereo sample from a single microphone (wild guess)?

[steve]

Microphone volume is set to 100% and the microphone boost is off.

The microphone boost usually needs to be ON.
That should fix the low recording level issue.

Do I need new sound card driver?

Internal (on-board) sound cards are generally low quality on PCs - it's one of the ways that they keep the price down.
The microphone inputs in particular tend to be poor, which is why there is such a thriving market for sound card upgrades (internal or external) and USB microphones (which bypass the sound card input altogether).

is it possible, that for some reason there are 2 microphones in my laptop (sony vaio)

Some laptops do have multiple microphones, but it's unusual. You said that you were getting the same problem on multiple machines and I very much doubt that they all have microphone arrays.

It looks like you may be recording from somewhere in Europe?
In the US the mains electricity is AC with a frequency of 60 Hz
In most of Europe the mains frequency is 50 Hz.
Your recording is picking up strong interference from the mains electricity. This can be seen as a high peak at 50 Hz, then strong harmonics at 100 and 200 Hz.

There is also a little "DC-Offset" which is caused by a DC bias voltage on the input. That's a fault on the sound card, but it's a fairly small error (though it shows up clearly on "Plot Spectrum" from the "Analyze" menu).

The mains hum is likely to be caused by either a bad connection, or from using "unshielded" cable between the microphone and the sound card input.
Audio cables are usually "co-axial" which means that the signal wire is surrounded by a wire mesh or foil sheath that shield it from electro-magnetic interference (EMI). Unshielded cables will pick up EMI, mostly in the form of a low hum. Because microphone signals are so small the interference can easily dominate the real signal.

The interference can be filtered out from the recording, but doing so will also take out part of your microphone signal so it is much better to fix the cause of the problem that to try and "repair" it later.