Difference between revisions of "Recording length"

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{{Introrel|As a free open source program, Audacity does not of course expire after you have recorded with it for a certain total length of time, and with the exception noted below for 1.2.x Audacity versions, there is no limit imposed by Audacity on the length of any individual recording. The length of time you can record for depends fundamentally on the disc space you have available, and that required disc space depends on the quality you record at.||[[TimedRecording|Timed Recording]]
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{{advice|This page has been transferred to the Audacity Manual - see [https://manual.audacityteam.org/o/man/faq_recording_how_to_s.html#remaining FAQ: What is the maximum recording length?] in the Manual for [https://web.audacityteam.org/download/ current Audacity].}}
* All our [[Recording Tips]]}}
 
 
 
 
 
__TOC__
 
=Recording time/disc space remaining=
 
 
 
When you record, the audio data is written to your hard disc. For example, if you just press the red Record button without having yet saved a Project, it's written to Audacity's temporary folder
 
(Beta 1.3.3 and later has a setting on the {{menu|Directories tab of Preferences}} to cache the recorded data to memory during the actual recording, with writing to the temporary folder occurring when recording is stopped). Therefore, the amount of time you can record for is always limited by the available disc 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 {{external|[http://audacity.sourceforge.net/download/ here]}} give a clear indication in the Status Bar at the bottom of the screen as to how much time you can record for, i.e. "disk space remains for recording ... xx hours xx minutes".
 
:[[Image:Diskspacerem.PNG|350px|Status Bar showing disk space remaining for recording]]<br clear="all" />
 
 
 
 
 
The time remaining is calculated on the basis of 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's preferable if you're intending to save a Project to save an empty Project before you start recording, with the {{menu|File > Save Project As...}} 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 {{menu|File > Save Project}} ('''''not''''' {{menu|File > Save Project As...}}) to update the Project. 
 
 
 
=Increasing disc space for longer recordings=
 
 
 
If you need more recording time you can:
 
 
 
# Obviously, free up some more disc 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 disc with more space on it. The location of Audacity's temporary folder can be changed on the {{menu|Directories tab of Preferences}}.
 
# Change the following settings in Preferences so that less disc space is used for recording:
 
## on the {{menu|Audio I/O tab}}, record in mono instead of stereo. This halves the disk space used.
 
## on the {{menu|Quality tab}}, reduce the Default Sample Format (i.e. the 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 affecting the quality too much. Generally for music, leave the Sample Rate at 44 100 Hz, but if you found say a sample rate of 22 050 Hz gave you acceptable quality, it would take half the disc space of a 44 100 Hz sample rate.
 
 
 
 
 
Here are some examples of disc space usage when recording at different quality settings:
 
 
 
* <span style="color:#CC9900">44 100 Hz, 32 bit, stereo = 20 MB of space per minute.</span> <span style="font-style:italic">44 100 Hz and 32 bit are Audacity's default settings when recording.</span>
 
* <span style="color:#CC9900">44 100 Hz, 16 bit, stereo = 10 MB per minute.</span><span style="font-style:italic"> This is CD quality recording.</span>
 
*<span style="color:#CC9900"> 22 050 Hz, 16 bit, mono = 2.5 MB per minute.</span>
 
 
 
 
 
Note that these disc space usages relate solely to the size of recorded data held by Audacity, not to the size of audio files exported from it. You need this space to record, but if you don't save an Audacity Project, the temporary data is deleted and the space released, as soon as you exit Audacity.
 
 
 
 
 
=Recordings over 13.5 hours=
 
 
 
If you are preparing to make a very long recording of a few hours or more in length, additional computer resource issues may be involved apart from disc space. These would include the need to have sufficient RAM and swap file space available (including taking steps to minimise memory use during the recording), and ensuring automated events such as system or program updates or screen savers are not able to disrupt a recording. Additionally, you need stable up-to-date sound device drivers properly matched to your hardware. See the tips at [[Managing Computer Resources and Drivers]] before starting a very long recording.    
 
 
 
Note there is a technical 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 44 100 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 (48 695 seconds), at a 44 100 Hz sample rate (44 100 samples per second), gives you 2 147 449 500 samples. This is a very close number to 2^31 (i.e. 2 to the power of 31) = 2 147 483 648.  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 2 147 483 648, and it follows that the length of time you can record for is then controlled by the chosen sample rate (given you have the disc space to record in the first place of course).
 
 
 
The solution if you want to record over 13.5 hours is thus to use the 1.3.3 Beta version of Audacity where the same values are stored as 64-bit values (even on 32-bit machines). Thus at 44 100 Hz sample rate you can get a maximum recording length of 58 000 000 000 hours(!).  Alternatively in 1.2.x  you can reduce the sample rate you are recording at by changing the Project Rate button bottom left of the Audacity screen. If for example you record at 22 050 Hz (which is generally acceptable for speech recordings) you can theoretically record for just over 27 hours.
 
 
 
[[Category:Tips]]
 

Latest revision as of 12:56, 21 August 2017

Warning icon This page has been transferred to the Audacity Manual - see FAQ: What is the maximum recording length? in the Manual for current Audacity.