Audio recording technique – some suggestions

by Bob Cunningham
 

The following is an excerpt – with minor editing – from an e-mail message I recently sent to someone who was about to make some audio recordings for submission to the audio archive. On 19 September 2000 I've modified the file to ask for a minimum sampling rate of 22,050 Hz in place of the 8,000 Hz I previously asked for:

If you use Windows and if you don't already have a good audio package, I recommend that you download GoldWave. Once you take awhile to learn to use it, it will save you a lot of trouble. It's shareware, so you don't have to pay for it unless you decide you're going to continue to use it.

I'm going to mention some things to watch out for. You may already know about them; in fact you may know a lot more about sound recording than I do. Please forgive me if I tell you something you already know.

  1. Be prepared to be repeatedly dissatisfied with what you record. Your first recording, or your second or seventh, may have pops, clicks, or hum, and it may be recorded at too high or too low a level. To get an idea of how many things can go wrong, listen to some of the recordings in the AUE Audio Archive. Some of them are barely adequate, typically containing too many pops and too much hum or other background noise.
  2. Talk across the mike rather than into it. Talking into the mike – that is, holding the mike directly in front of your mouth – tends to produce pops when you pronounce words starting with 'p'. Other plosives are also exaggerated when you face the mike directly. You may have noticed in televised recording sessions on TV that some vocalists have a wire mesh between the microphone and their mouth. When you pronounce one variety of 'p', you tend to spit; spit hitting the microphone results in pops in the recording.
  3. Don't hold the mike in your hand; put it on a stand. Holding the mike in your hand can result in annoying rubbing noises as the mike shifts in your hand.
  4. Keep the mike away from fluorescent-light fixtures, computer air vents, and any other sources of noise you might have. The room can seem quiet to you while the mike picks up all sorts of noises you wouldn't suspect.
  5. If you have noise that you can't trace to a source, it may be that the mike is picking up vibration from the surface the stand is sitting on. Try setting the stand on a surface that isn't vibrating, or try putting a cushion of some sort – maybe a mouse pad – between the vibrating surface and the mike stand.
  6. Choose: sampling rate 22,050 Hz, 'mono', 8 bit. It would be nice to be able to use a higher sampling rate, but the size of the file is directly proportional to sampling rate, and it's good to save as much Web-site room as possible. The sampling rate of 22,050 Hz is a minimum, though. It will be used to make an MP3 file at that sampling rate. For large files, the sampling rate may be reduced for WAV files.
  7. Watch the oscilloscope display on the GoldWave display while you are recording. You can tell by watching if your level is too low or too high. Try to adjust the level so that you're filling up most of the available amplitude range without clipping. Clipping appears as extended flat tops on the waveform. Keeping the recording level as high as possible without clipping gives the recorded voice an advantage over quantization noise and other internal noise.
  8. Adjust the recording level so that you can get the mike close to your mouth without overloading. That gives your voice an advantage over ambient noise.
  9. Listen to the recording after you've made it. If you hear anything you're not pleased with, try to figure out what went wrong. Take appropriate corrective measures and record again. See if you can make the quality of your recording better than any of the ones in the AUE Audio Archive.

If something about the facilities you have won't let you record at 22.05 kHz, go ahead and record at a higher sampling frequency. The webmaster can use GoldWave to resample the files after he gets them.

If you have any questions, or if you have comments about my suggestions, please feel free to send e-mail to me.