How can I record piano on a laptop without high frequency wahwah?

Question

Example:

http://soundcloud.com/andrewclow/phases-for-piano

(That's particularly bad example, via mp3 and the built in mic, the effect is always there before converting and with a better microphone. )

When I'm recording piano, I get a sort of slow wahwahwah effect just at high frequencies, that makes the piano have a sort of metallic sound, particularly in quieter sections with less bass (although that might just mean it's more perceptible then). It's also audible in the second or two of hiss before I start playing, and there's a noticible change in the tone of that hiss as we near actual music.

Currently I'm using Audacity with default settings on my XP netbook but was surprised to find the same problem with Audacity on my colleague's new, high spec Windows7 ultrabook. However, the effect isn't noticibly there with the same microphone and a straight-to-mp3 dictaphone, which surprises me.

I've tried it with and without plugging in a small microphone, and changing between realtek and the other option for audio input in Audacity, and I've tried using a much higher sampling rate.

• Is the problem likely to be the sound card on the laptop?
• If so, what should I ask for in a new laptop (which I'm planning in the next couple of months anyway), or should I get an external USB soundcard?
• Is the problem likely to be in Audacity? If so, what settings should I change for piano recording, or what other free or cheap recording software is both straightforward and good.
• Is there something else I haven't thought of?

(The question What do I need to make reasonable quality amateur recordings of vocals/piano to put on Youtube? has some good advice about external hardware if that's the best solution, but if I can do it with existing PC hardware, or with an intelligent choice of a new laptop, that would be great.)

Answer 1

Never expect to get usable quality when recording through laptop built-in sound hardware, be it the microphone or just the preamp and AD.

A microphone that you can operate at all on your sound card's mic input is almost certainly not suited for piano recording; virtually all such microphones require 48V phantom power.

But you say this problem doesn't occur with the same mic when using another recorder, so it's really an issue of your laptop itself. It sounds very much digital (though it's a bit hard to tell: this record you posted is apparently a very strongly compressed .mp3?), so it's most likely about the AD. I can't say what exactly, but honestly it doesn't matter much because again: you won't get good results with that anyway, anyway. Do get yourself a USB audio interface and a nice pair of condenser microphones, you don't have to spend that much and you'll be able to do really nice recordings with the right setup.

All that said, I actually happen to rather like this strange sound in your example: it adds an eerie, hypnotic quality to the piece that IMO fits really well. Sometimes worse is better!

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Edit, after quite a while...

Not sure if I didn't notice this back then, but now I do: the "wah wah" sounds a lot like an automatic de-noising filter – which obviously fits perfectly to what you say about the sound of the hiss changing when the piano comes in. Indeed basing denoising is often done with a simple low-pass filter, and wah-wah is nothing else but a time-varying resonant low-pass.

This doesn't change much about the advice: don't use consumer-grade sound cards for recording, the fact that this gives you such strange counter-productive sound "improvements" like low-quality denoising is a major reason for that.

Answer 2

This sounds like a phase effect rather than a wah effect. My first though is that you are getting some interaction between the "direct sound" of the piano and reflected sound. I think this is called "comb filtering" and in this particular case is undesirable.

Experiment by moving your microphone position. Also look into "undesirable phase problem piano microphone" and/or "comb filtering problem"

Answer 3

How recently has your piano been tuned? The higher notes have two or three strings per note, so it is possible that the high-frequency phasing is because some of those strings are out of tune by a few cents.

Two other things to consider:

• Are you using a single microphone, or either a pair or a "stereo" mic? If you are recording in stereo, try moving the microphones around until the phasing goes away.

• Is the piano in a room with flat, hard surfaces? If so, you will get strong reflections that may be responsible for phasing. Try moving the piano to a larger room, or try hanging up large heavy drapes, adding tall plants or otherwise breaking up the flat surfaces.

Answer 4

Now, I am not familiar enough with Audacity to say for sure, and I can't actually see or hear what's going on, but it sounds to me like the problem is that Audacity is recording straight to a compressed format. Try recording to, for example, 16- or 24-bit WAV file. Once that's done, you can audition it to make sure it sounds right. If it still sounds problematic, then I am wrong and something else is the problem :(

If I am right and your goal is to create an MP3 or AAC or other compressed format, you should be able to do that at the end, using an "export" or "save" command.

It's possible that this is also a microphone placement issue, but that usually results in a hallow sound, not a sound that changes over time, which is what you are describing.

It is unlikely that what you are describing is caused by the soundcard. External USB is almost always a positive upgrade from built-in audio, but that is unlikely to solve this particular issue.