Development [LWN.net]

Multi-track recording with Audacity

Audacity is one of the more popular audio editing systems for Linux. It features a straightforward user interface, recording and playback capabilities, and a number of useful editing options. Your author decided to see if Audacity was capable of working as a basic multi-track music recording system.

[Audacity] The hardware used for this experiment consisted of a fairly ancient 700 Mhz Pentium 3 box with 384 MB of RAM and an old IBM 20 GB hard drive. This machine was purchased second-hand at a yard sale for a mere $10. The sound card was an older no-frills Creative Labs model CT4810 PCI device.

Audio was generated with an electric guitar feeding into a guitar amplifier. The amplifier's line out was connected to the sound card's line in with a mono to stereo adapter plug.

The software consisted of the Ubuntu 6.06 LTS "Dapper Drake" distribution running the default stable version 1.2.4 of Audacity.

Setting up Audacity for multi-track recording took a bit of tweaking. The sample representation was changed to 16 bit integer mode and the audio i/o setting was changed to 2 channel (Stereo). The "Play other tracks while recording new one" setting was enabled, this is the critical feature that allows "sound-on-sound" recording. Tests using the default 32 bit floating point sample representation, single track recording and software play-through all resulted in serious dropouts and time distortion on the recordings. These problems also occurred with a more full-featured Sound Blaster Live card in the same system.

Once the correct settings were applied, recording was a simple matter of setting the input level below the clipping point using the input monitor VU meters, and pressing the record button. As with most multi-track recording, it was necessary to record, erase and retry most of the tracks. Audacity makes listening to and re-recording tracks easy, the rewind/play/stop/record buttons are identical to those found on a standard tape recorder, and the undo function (Control-Z) is used to remove a badly recorded track.

One minor problem showed up when playing back while recording. During the recording of the second track pair, the sound from the previously recorded first track pair made clicks and had some short sound dropouts. Fortunately, this problem only occurred while recording, the clicks disappeared when all of the tracks were played back simultaneously. This seemed to get worse as more tracks were added and may be symptomatic of insufficient CPU speed.

Once the desired number of tracks (3 stereo pairs) was correctly recorded, it was time to do a mixdown. This is a simple manner of setting the left/right pan setting for each stereo track pair and adjusting the output levels for a good volume balance between track pairs. The default 0 db track volume level produced audible clipping when multiple tracks were summed together, so it was necessary to attenuate all of the tracks by a few db. The final results can be easily exported to wav, ogg or mp3 format stereo files. The results of this (highly amateur) recording effort can be heard in this short ogg file.

This version of Audacity is a bit unpolished for multi-track audio recording work, but with a bit of effort, it can be made to function as well as an analog tape recorder. The output quality is very good, considering the inexpensive audio equipment that was used. Some of the editing effects such as track volume normalization, fade in/out and silencing of arbitrary sections make production of quality recordings much easier than with older analog equipment. Anyone who has ever waited for a reel-to-reel recorder to rewind will truly appreciate the instantaneous transport controls.

The inability to record mono tracks is an obvious deficiency, the recordings are twice as large as they should be, the screen fills up rather quickly and the total unique track count will be reduced for a given power of CPU. Despite this, Audacity can allow a junker computer to be turned into a useful piece of audio gear with a trivial amount of installation effort.

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