General introduction to recording
Jamie Bathgate gives a general introduction to sound and how we record it, as well as an introduction to the PPLS studio in the basement of Appleton Tower
Sound is vibration. When we speak, or indeed make any kind of sound, we create vibrations in the air. These vibrations, or sound waves, travel through the air to your eardum and move it back and forth. Your eardrum converts these vibrations into nerve signals. These signals are what you recognise as sound.
The recording process
There are three steps involved in sound reproduction:
- Capturing: A microphone contains a "skin" of sorts, called a diaphragm. Much like your eardrums, the diaphragm translates vibrations into electrical signals.
- Encoding: A recorder translates and stores this electrical signal on a medium, such as grooves in a vinyl record, magnetic particles on a cassette tape, or as binary code on a CD.
- Playback: A player reads a medium and translates its information back into an electrical signal. An amplifier gives this signal a boost and sends it to a speaker. The speaker has a cone which vibrates back and forth in time with the electrical signal to reproduce the recorded sound.
In short, recording converts sound to electrical signal and then stores this signal on media. Playback reads the signal from media and reproduces the recorded sound.
The PPLS studio
The recording studio is located in the basement of the Appleton Tower, room B.Z.31 and maintained by Jamie Bathgate. He is available to assist with recordings if you include this requirement when you make your booking.
In the PPLS studio, we use the three steps described above to make high quality audio recordings of the human voice for analysis.
- Capturing: There are two rooms in the studio: an isolation booth for the subject and a control room where the experimenter controls recording. In the isolation booth use a Shure SM7 cardioid pattern microphone. This microphone is directional; it records sounds from the front and rejects sounds from the back and sides to capture the subject’s voice clearly.
- Encoding: A cable runs from the microphone to a preamp which boosts the signal. Another cable runs from the preamp, through a wall and into a device called Digidesign 003 in the control room. The Digidesign 003 has sliders and knobs to control recording level and playback volume. The Digidesign 003 takes the signal from the isolation booth and feeds it into the iMac, where we use software called ProTools to record, playback and edit it, then save it on the iMac’s hard drive as WAV audio files.
- Playback: The computer is connected to speakers via the Digidesign 003. When the audio file is played back on the computer, it is passed through the Digidesign 003 and converted back to an electrical signal. The speakers convert this electrical signal back into sound.
In the PPLS studio we ensure that every recording is of high quality. It is standard procedure to record everything at higher-than-CD-quality; with a sample rate of 48khz, and a bit depth of 16 bit.
The recording studio can appear daunting with all of its cables and boxes and knobs and switches and sliders and more cables, but making a recording is actually quite simple. Although Jamie can be there to help you record, the studio has been designed in a way to allow you to make your own recordings.
In a typical set-up, you (as the experimenter) sit in the control room listening to your subject via two speakers, and recording them while they sit in the isolation booth talking into the microphone. The isolation booth is designed to reduce unwanted noise that would affect the quality of the audio recording, through sound-treatment measures like wall and ceiling panels that reduce sound reflection, and particularly thick walls, doors and flooring to block noise from outside the booth. A talkback microphone in the control room lets you talk to the subject in the soundproofed booth via their headphones, while a window allows you to gesture to each other.
If you are a first time user, ask Jamie to train you in the studio ahead of your first session. After a few minutes, you’ll be up and running!
Field recording set-up
You may need to venture into "the field" to make some onsite recordings or record people in an external environment. The premise is the same: use a microphone to capture the sound and save it to a device. However, you also need to minimise unwanted noise on your recording. Consider the best way to get away from any noise sources such as ticking clocks, traffic, and my wife.
We keep a range of equipment to lend specifically for this purpose, with different microphones and recording devices for different situations. What you use depends on the desired result, and how you then intend to use the data. You can ask Jamie to help you decide what set up will work best for your project. You can also refer to our Guide to Field Recording for an overview of equipment types.
ADC: Analogue to Digital Converter. A device that converts analogue signals to digital signals.
amplifier: A device used to boost the strength of an electrical signal.
binary code: A language made up of 0s and 1s (known as bits) to represent information, including audio, in a computer.
bit depth: The more bits (see above) that a computer uses to store a sound, the clearer that sound recording will be. We record at 16 bit, the same as CD quality.
cardoid microphone: A directional microphone which records sound from the front and rejects most sound from the rear and the sides, in a heart shaped pattern.
control room: A room where the recording equipment is housed and operated.
hard disk: Magnetic disk used to store data, usually in a computer.
isolation booth: A soundproofed room in which a subject is recorded.
master: An original recording from which copies can be made.
preamp: A small amplifier that is used to raise the level (gain) on a signal before the main amplifier in a system.
sample rate: Describes how frequently an analogue audio signal is sampled as it is converted into a digital format. 44.1 kHz is the standard sample rate for CDs, and 48 kHz offers even quality recording. While a recorded sound can never be 100% identical to the original, a higher sample rate means a more accurate recording.
WAV: A standard computer audio file format. WAV sound files end with a .wav extension and can be played by nearly all sound applications, e.g. Windows Media Player, Audacity and Quicktime.
talkback: A microphone set up to talk to the subject through their headphones in the control room.