Difference between revisions of "Recording length"

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(Long recordings: reply to Gale:)
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{{ednote|'''Peter 4May14:''' [[ToDo-T]] This page is a potential candidate for moving into the Manual.  }}
{{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].}}
{{Introrel|Audacity lets you record for as long and as often as you need, subject to the disk space you have available. <p>The disk space needed for recording depends on the quality ([[Sample Rates|sample rate]]  and [[Bit Depth|bit depth]]) at which you record.||All our [[Recording Tips]]</p>}}
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==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 {{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: 
:[[Image:Diskspacerem.PNG|350px|Status Bar showing disk space remaining for recording]]<br clear="all" />
{{ednote|'''Peter 1May14:''' [[ToDo-1]] image needs updating for latest version - snap-to has changed. }}
The time remaining depends on the current space on the drive, and on the quality (sample rate and bit depth) you are recording at. 
{{alert|1=Audacity has an option on the {{menu|Directories tab of Preferences}} to cache the recorded data to memory during recording: writing to the temporary folder only occurs after recording is stopped. This can be useful if your temporary folder resides on a slow network drive, but:
* This option also caches most audio data including project edits, so can cause crashes
* If the recording crashes before it is stopped it '''cannot''' be recovered.}}
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 {{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. 
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==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 any .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 {{menu|Directories tab of Preferences}}.
# Audacity only uses uncompressed (so lossless) [http://en.wikipedia.org/wiki/Pulse-code_modulation 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 {{menu|Devices tab}}, record in '''mono''' instead of stereo. This halves the disk space used.
## on the {{menu|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 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, {{menu|File > 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 {{menu|View  > History}} and discard the Undo levels you do not need.
{{Hint|1='''Examples of disk space usage when recording and editing at different quality settings:'''
* 44100 Hz, 32 bit, stereo = 20 MB of space per minute. <span style="color:#333300;font-style:italic">44 100 Hz and 32-bit are Audacity's default quality settings</span>
* 44100 Hz, 16 bit, stereo = 10 MB per minute.<span style="color:#333300;font-style:italic"> CD quality</span>
* 22050 Hz, 8 bit, mono = 1.25 MB per minute. <span style="color:#333300;font-style:italic"> This would be generally acceptable for speech recordings from lower quality sources</span>}}
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.
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 don't save an Audacity Project, the temporary data is deleted and the space released as soon as you exit Audacity.
{{Hint|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 [http://en.wikipedia.org/wiki/RAM RAM] and swap file space available, and ensuring automated events such as system or program updates or screen savers are not able to disrupt a recording. For details, see [[Managing Computer Resources and Drivers]]. Having stable, [[Updating Sound Device Drivers|up-to-date sound device drivers]] properly matched to your hardware also becomes more important . }}     
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==Long recordings ==
Current Audacity stores samples as 64-bit values (even on 32-bit machines). Therefore unlike some legacy 1.2.x and 1.3.x versions of Audacity, 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 44100 Hz sample rate).
44100 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).
{{ednote|'''Gale 12May14:''' [[ToDo-1]] Make the context of the below historical after 2.0.6. Should not the meat of the content  though be moved to legacy Wiki at that time?
*'''Peter 12May14:''' Surely we can move the "meat of the content" into Legacy Wiki right now - as Legacy Wiki is valid for versions up to and including 2.0.5.  When 2.0.6 is released we can deprecate the 2.0.5 content.
===Problem with long recordings saved as projects===
{{alert|'''Audacity projects containing more than 2^31 samples will re-open empty''' with the entire data being seen as "orphaned files" (although the data "appears" to be in the correct location expected by the AUP file). '''Workarounds:'''
* '''Before saving or closing the project, export the recordings to WAV, AIFF or lossless audio files of appropriate size''', or cut and paste sections of the recording containing less than 2^31 samples to new Audacity projects and save those.
* '''To fix a saved project that is at or in excess of the 2^31 samples limit,''' open the project in the latest [[Nightly Builds|2.0.6-alpha]]. The project should open correctly in that build if it does not have any other problems.}}
==== Further notes on large audio files ====
WAV files should not exceed 2 GB in size for practical purposes, and the absolute maximum is 4 GB. For longer lossless files you can use [[FLAC]] on Mac or Linux (there is a 2 GB size limit in Windows). On any platform in Audacity 1.3.13 or later you can export larger lossless files up to about 16 [http://en.wikipedia.org/wiki/Exabyte exabytes] in size using [http://en.wikipedia.org/wiki/RF64 RF64]. RF64 will be about the same size as [[WAV]] files (that is, about twice as large as FLAC). To export as RF64, choose "Other uncompressed files" then click {{button|Options...}}.
==== Further help for users of 2.0.5 or earlier ====
If you don't use 2.0.6-alpha or have problems reopening the excessively long project, you may try the following.
* '''Split the project into smaller projects''', adjusting each AUP file so that the "h" value is zero, the correct _data folder is pointed to and the "numsamples" and "waveblock start" values are corrected (a script must be used to perform this correction because thousands of values will be involved). See http://forum.audacityteam.org/viewtopic.php?p=214543#p214543.
* '''Do not use the AUP file but split the data into smaller _data folders.''' Each folder should not exceed 1&nbsp;GB in size. If the project was created in Audacity 1.3 or later, time-sort the AU files in each folder then rename the files into a consecutive sequence. Use the Audacity 1.2 Recovery Utility to recover each folder to a separate WAV file (one WAV per stereo channel), then import the WAV files into Audacity and join them together. <p>This method may cause some sections of left and right stereo channels to be transposed on Windows FAT32, Mac OS X and Linux (ext3 or earlier) file systems due to their limited timestamp granularity. Also, only unedited recordings can be recovered in correct timeline position by this method. See the [[Crash_Recovery#Automatic_recovery_tools|Crash Recovery]] page for details. </p> 

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.