|Audacity lets you record for as long and as often as you need, subject to the disk space you have available, and (in 1.2.x), a limit of 13.5 hours at default 44100 Hz sample rate. The disk space needed for recording depends on the quality (sample rate and bit depth) you record at.
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's 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. Older versions of Audacity had a confusing "recording time remaining" message which did not make this clear. However current versions of Audacity which you can always download give a clear indication in the Status Bar at the bottom of the screen as to how much time you can record for:
The time remaining depends on the current space on the drive, and on the quality (sample rate and bit depth) you are recording at.
Although there are rarely problems if you record to Audacity's temporary folder and then save the recording as an Audacity Project, it may be preferable if you're intending to save a Project to save an empty Project before you start recording, with the command. That way, the recorded data will be saved to a permanent location in the Project's _data folder. When the recording is over, and now and again thereafter, use (not ) to update the Project.
Increasing disk space for longer recordings
To get more recording time:
- Obviously, free up some more disk space. One good way to do that is to ensure you delete your old Audacity Projects (the .aup and .aup.bak files and the _data folders) as soon as you've finished the Project and are sure you won't need to export any more files from it.
- Save the Project you're 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 .
- 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 , record in mono instead of stereo. This halves the disk space used.
- on the , 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 44100 Hz, but if 22050 Hz gives acceptable quality, it takes only half the disk space of 44100 Hz.
- 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, , exit Audacity and relaunch it. This will clear out the space being used by the Undo mechanism. Alternatively, leave the project open, click and discard the Undo levels you do not need.
- 44100 Hz, 32 bit, stereo = 20 MB of space per minute. 44 100 Hz and 32 bit are Audacity's default quality settings
- 44100 Hz, 16 bit, stereo = 10 MB per minute. CD quality
- 22050 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. 44100 Hz gives a theoretical maximum of less than 22kHz that can be captured. A sample rate of 22050 Hz gives you less than 11kHz. 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 22050 Hz, 8 bit recording would rival the sound of a good quality cassette tape.
Recordings over 13.5 hours
There is a limit to recording time in Audacity 1.2.x which is determined by the maximum number of audio samples it can store. When recording at Audacity's default 44100 Hz sample rate this implies a maximum recording time of about 13 hours, 31 minutes, 35 seconds. The reason is that this length of time (48695 seconds), at a 44100 Hz sample rate (44100 samples per second), gives you 2 147 449500 samples. This is a very close number to 2^31 (i.e. 2 to the power of 31) = 2 147 483648. 2^31 is the biggest positive number that a 32-bit integer can represent, and in the 1.2.x series of Audacity the position in the file is stored as an integer, which will be a 32-bit signed value. So the theoretical maximum number of samples Audacity can store is 2 147 483648, and it follows that the length of time you can record for is then controlled by the chosen sample rate (given you have the disk space to record in the first place of course).
In principle, the solution to recording over 13.5 hours is to use the latest 1.3 Beta version of Audacity. Here, samples are stored as 64-bit values (even on 32-bit machines), which at 44100 Hz sample rate offers a maximum recording length of a mere 58 billion hours. Whilst we believed 64 bit storage worked properly in 1.3.3 and later, some reports in early 2008 suggested that recordings were still coming up against the 2^31 limit. Our development code was fully converted to 64 bit sample counts in July 2008, so long recordings should work again in our Nightly Builds and in 1.3.6 Beta onwards.
If you need/prefer to use Audacity 1.2.x, you can increase recording time over 13.5 hours by reducing the sample rate of the recording. To do this, changing the Project Rate button bottom left of the Audacity screen. For example, recording at 22050 Hz permits a theoretical recording time of just over 27 hours.