Audio Recording Terms

Audio I/O Device

This tutorial often refers to your computer's Audio I/O (Input/Output) Device. This device is used for playing back audio from your computer and recording audio to your computer. In the past this device was most often referred to as a "sound card". We shy away from this term because currently many PC's and laptops have a built-in audio I/O device that is not an add-on component like a sound card is. However, soundcards are still in wide use. In fact it is most common for the built-in audio I/O device to be of a standard audio quality while soundcards are often used when higher quality or performance is needed. In addition to these two devices there are also external audio I/O devices that interface with the computer via USB or Firewire. These devices are often popular with laptop users, since the standard audio I/O devices often limit the user to a mic only input. All of these devices (built-in I/O devices, soundcards and USB/Firewire devices) are capable of CD quality audio and work well with the Acoustic Labs Multitrack Recorder.

Multitrack Recording

Multitrack recording is the process of recording each sound (or voice) of an audio production onto an independent track. The tracks are kept independent so each one can be manipulated individually. Once the user is satisfied with the overall sound, the multitrack recording can be mixed down to a single audio track such as an audio file or song on a CD.

As an example, let's use the members of a band creating a song. The band has a singer, guitar player, bass guitar player and drummer. Each musician will record their instrument on a separate track. If one of the musicians makes a mistake, they can go back and re-record their track (or part of their track) without affecting any of the other tracks.

The volume level of each track can be modified independently, effects can be added or removed and all types of editing can be performed only affecting the single voice or instrument. More instruments can be added - as band members record new tracks, the existing tracks play back simultaneously.

Once the band is satisfied with how their song sounds, they can use the "Mixdown" feature to mix all of the tracks down to a single audio track that can be saved as a wave or MP3 file. The song can then be burnt to a CD, transferred over the web or put on an iPod or similar device. All of this is included in and can be accomplished with the Acoustic Labs Multitrack Recorder.

Digital Audio and Sampling

When recording audio, the computer's audio I/O device measures and records the intensity of the given sound many times per second. This is known as sampling. As an example, CD quality audio is sampled at a rate of 44,100 Hz, which corresponds to taking 44,100 samples every second. This sampled version of the original sound is known as digital audio, or it is said that the original sound has been "digitized". The original sound is now represented by the samples taken. When playing back audio, the computer's audio I/O device recreates the sound by playing back these samples. The audio quality increases as the sample rate increases. This is because as we increase the number of samples, we increase the amount of specific information we have for the sound. It is no coincidence that 44,100 samples per second was chosen as CD quality. Due to waveform characteristics, a sampled waveform (such as audio) can contain frequencies only as high as half the sample rate. Since the human ear cannot hear frequencies above 22,000 Hz, the 44,100 Hz digitized audio generally recreates the same sound humans hear in the real world.

Audio Waveform Editing

Audio waveform editing refers to modifying digitized audio. As fully described above in the topic "Digital Audio and Sampling", the computer's audio I/O device turns real world audio into a digitized version of the sound that is made up of many sample points. This sample point data can be edited by selecting various sections of audio and performing cut, copy, paste and other editing features and effects described in full in later sections of this manual. Also, Section 6: Waveform Navigating describes in full detail how to use the mouse to select areas of the waveform for editing. The Acoustic Labs Multitrack Recorder is capable of zooming in to and editing at the sample level - the highest magnification level possible for digital audio. This allows for very specific and precise editing capabilities as the user can modify sections of audio that are less than one millisecond in length.

Mixing Down

Mixing Down is the act of combining two or more tracks into a single track. The current level settings are taken into consideration so that both tracks mixed together sound exactly the same as they did when they were separate, independent tracks. There are two main reasons why you would want to use a mix down feature. The first reason would be that if the user has finished the project and wishes to either burn it to a CD, or convert it to a sound file to transfer across the web, email or to an iPod or similar device. Another common reason for mixing down audio tracks is to "free up" tracks or make more tracks available. By freeing up additional tracks, the user is able to record to the tracks that have been freed.

For example, if you've recorded audio on all eight tracks and you wish to record additional tracks, you could mix down any completed tracks to one single track. In this example, assume that tracks one through four are completely recorded and need no additional editing. You can mixdown tracks one, two, three and four to track one. Track one will now contain all the mixed audio of track one through four and tracks two, three and four will now be available for new recordings.