Recording audio using a mixer board
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This how-to describes how to record audio when using a microphone that is connected to your computer through a mixer board (or mixer) and which settings to use.
This how-to is especially useful to read, if you have encountered problems with clipping.
It is always advisable to make a test recording and see if the audio quality meets your expectations.
First of all, read the how-to for recording audio in the phonetics lab, as this procedure works roughly the same and ignore from the chapter power-On Equipment sections 1 through 4, because the hardware you are using is probably a little different from that in the phonetics lab. Instead, follow the instructions in the the how-to for the system you are currently using.
You can also skip the chapter Recording Level Instructions, as these instructions are hardware specific as well.
Though most microphones can’t be positioned by yourself, as they are attached to a headset, we advice you to read through the chapter Microphone Position as well, as a few common mistakes with recording human voice are listed there.
Connecting the proper hardware
On all computers on which audio recording is possible, a microphone is connected to a mixer that is itself connected to the computer. This is the default wiring and if you think something is wrong in a specific setup, please contact technical support in room 0.09. Please do not change the wiring yourself, you can short-circuit some expensive devices!
- Check to which channel the microphone is connected. This should be the first channel, but it isn’t too big a problem if it’s any of the other channels.
- Turn down the gain dial completely on all other channels. This is the black dial at the top of the channel row (just below where the microphone is usually plugged in to the mixer). Also turn down the volume dial on all channels not in use. This will prevent noise from other channels entering your audio stream.
To make a good recording, one of the things you should take into account is clipping (e.g. the input goes beyond what the computer can differentiate between, see wikipedia) which will create audio recordings with serious artifacts.
To prevent clipping you have to make sure the loudest input never goes near or to the end of the input level meter. For this you have to calibrate both dials on the mixer and settings on the PC.
How to set the gain to the proper level on the mixer
- Set the master output / fader for the main volume to 0 dB. (The volume fader is the red slider on the right side of the mixer.) It is set to 0 dB if the white dash in the middle of the fader is at the same level of the dash that has a 0 next to it.
- Set the volume dial on the channel that your microphone is connected to, to maximum.
- Ask your participant to make the same kind of sounds you would have him make during the test. If the participant will be reading things out loud, give him a practice tekst to read. If he will need to produce sounds, ask him to produce similar sounds at this point.
- Above the main volume fader, two rows of LEDs are visible. These lights indicate the input level of your signal. The louder the signal, the more LEDs will light up. For a perfect input signal, you want your signal to be as loud as possible, without any of the red LED’s lighting up. A n input level that is to low leads to a bad signal/noise ratio. Every channel on the mixer has another single red LED. This LED will light up if the signal on that specific channel is too strong. We will use these LEDs to test our input signal.
- While your participant is making the sounds you asked him for, slowly open up the gain dial. You will see that the LEDs above the fader start flashing to indicate the signal strength. By the time the top row of green LEDs lights up, don’t open the gain any further. Make sure that the red LEDs never light up not even if the participant suddenly raises his voice or makes strange sounds. If it does, tune the gain down a bit and re-check. Do this until you are at an balanced input level; it should be loud enough while not leading to clipping.
- As final step, make sure that the peak LED of the channel’ volume dail is not flashing during normal sound production. If it does, tune down the volume and reapeat from step 4.
You have now set the input signal on the mixer. However, this signal is also sent to the computer which has to process it as well. That is why we have to repeat some of these steps on the computer.
First of all, open Audacity and make sure all the recording settings are correct (see the how-tos for your current system for the exact settings).
How to set the gain to the proper level on the Computer
- Ask your participant to make the same sound as before again.
- Start a recording in Audacity and make sure you receive a signal by checking if you see a waveform appear, rather than just a flat, blue line.
- Audacity provides an input level meter which works roughly the same as the input level meter above the main volume fader on the mixer. Instead of working with LEDs, the input level meter of audacity shows two blue bars that turn red in the end if the signal is too loud. Every time a signal is received that is louder than the one before, a small red bar remains visible, so you can see what your maximum level is.
- We want to change the input level of Audacity such that the maximum volume is received, without clipping to occur. We do this by checking the input level meter in the same way as we did on the mixer. Try to get it as high as possible, without it turning red!
- Adjust the input signal level. This can be done either by moving the slider next to the microphone symbol in the top bar of Audacity slowly to the left, or by sliding the main volume fader on the mixer down slowly. Use either one, but not both!
If you receive a strong signal without the input level meter turning red, your signal should be alright. You can start recording now!
If not, keep adjusting the slider or the fader, until the signal is good.
If you have followed these steps correctly, you should now be able to start a recording. The recording this will produce should contain a clear and loud audio without clipping or too much noise.
This way you can spot problems with the audio early on.
To start the actual recording, read the chapter Recording in the recording audio in the phonetics lab how-to and follow this procedure.
If you can’t get the sound right or have a problem with the audio files, don’t hesitate to contact technical support in 0.09 to see what they can do for you!