Recording length

From Audacity Development Manual
Jump to: navigation, search
Audacity lets you record for as long and as often as you need, subject to the disk space you have available.

The disk space needed for recording depends on the quality (sample rate and bit depth/sample format) at which you record.

Recording time/disk space remaining

When recording, the audio data is written to your hard disk. For example, if you just press the red Record button without having yet saved a Project, it is written to Audacity's temporary folder. Therefore, the amount of time you can record for is limited by the available disk space on the drive you are writing to. Audacity lets you know the amount of time you can record for based on that remaining space, giving a clear indication in the Status Bar at the bottom of the screen as to how much time you can record for:

Status Bar Disc space remaining.png

The time remaining depends on the current space on the drive, and on the quality (sample rate and sample format/bit depth) at which you are recording.

If you record to Audacity's temporary folder and then save the recording as an Audacity Project this will take longer as the project file has to be copied from the temporary folder to the proper folder.

Thus it may be preferable if you are intending to save a Project to save an empty Project before you start recording, with the

That way, the recorded data will be directly saved to a permanent location/folder in your file structure.

When the recording is over, and now and again during editing, use File > Save Project > Save Project (not File > Save Project As...) to update the Project.

Increasing disk space for longer recordings

To get more recording time:

  1. Obviously, free up some more disk space. One good way to do that is to ensure you delete your old Audacity Projects as soon as you have finished the Project and are sure you will not need to export any more files from it.
  2. Save the Project you are starting (or change the location of Audacity's temporary folder) to a disk with more space on it. The location of Audacity's temporary folder can be changed on the Directories tab of Preferences.
  3. Audacity only uses uncompressed (so lossless) PCM audio data for recording and editing, but the amount of disk space consumed can be reduced by changing the following settings in Preferences:
    • on the Devices tab, record in mono instead of stereo. This halves the disk space used.
    • on the Quality tab, reduce the Default Sample Format (bit depth) from 32-bit float to 16-bit, which again halves the disk space used. In speech recordings you may also be able to reduce the Default Sample Rate without significantly affecting the quality. Generally for music, leave the Sample Rate at 44,100 Hz, but if 22,050 Hz gives acceptable quality, it takes only half the disk space of 44100 Hz.
  4. Note that because unlimited undo is available in an Audacity session, editing a project itself uses disk space. To reduce the space a project is taking, File > Save Project > Save Project, exit Audacity and relaunch it. This will clear out the space being used by the Undo mechanism. Alternatively, leave the project open, click View > History and discard the Undo levels you do not need.
Examples of disk space usage when recording and editing at different quality settings:
  • 44,100 Hz, 32-bit, stereo = 20 MB of space per minute. 44100 Hz and 32-bit are Audacity's default quality settings
  • 44,100 Hz, 16-bit, stereo = 10 MB per minute. CD quality
  • 22,050 Hz, 8-bit, mono = 1.25 MB per minute. This would be generally acceptable for speech recordings from lower quality sources

Note that reducing the sample rate will reduce the audio frequency limit. 44,100 Hz gives a theoretical maximum of less than 22,050 Hz that can be captured. A sample rate of 22,050 Hz gives you less than 11,025 Hz. For speech, you can take out the high frequencies without much loss of intelligibility. Likewise, reducing the bit depth reduces the dynamic range of the audio. For example, 16-bit gives a whopping 96dB of dynamic range. 8-bit recording reduces dynamic range to 48dB. A 22,050 Hz, 8-bit recording would rival the sound of a good quality cassette tape.

Note that disk space usage above relates solely to the size of audio data held by Audacity, not to the size of audio files exported from it. You need this space to record and edit, but if you do not save an Audacity Project, the temporary data is deleted and the space released as soon as you exit Audacity.

When making a longer recording of a few hours or more, other computer resource issues may be involved apart from disk space. These include the need to have sufficient RAM and swap file space available, and ensuring automated events such as system or application updates or screen savers are not able to disrupt a recording. For details, see Managing Computer Resources and Drivers in the Audacity Wiki. Having stable, up-to-date sound device drivers properly matched to your hardware also becomes more important. See this page in the Audacity Wiki for details.

Long recordings

Audacity stores samples as 64-bit values (even on 32-bit machines); therefore there is no inherent 32-bit limitation that recordings may not exceed 2^31 samples in length (which is for example just over 13.5 hours at 44,100 Hz sample rate).

44,100 Hz now offers a theoretical maximum recording length of a mere 58 billion hours or more than 6.6 years (if you have the disk space).