Bit Depth

From Audacity Wiki
Revision as of 18:28, 9 October 2007 by NT (talk | contribs) (created)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

Dynamic Range

The bit depth chosen for recording limits the dynamic range of the recording. (Other factors in the audio chain may also limit this, so more bits often will not produce a better recording.)

  • CD audio (.cda) uses 16 bits for good dynamic range and very low noise
  • Cassettes and players vary, but are in the region of 8 bit resolution, often less.


Computer Effects

Bit resolution affects file size. All other things being equal, a 32 bit file is twice the size of a 16 bit file, and an 8 bit file half the size of a 16 bit one.

Bit resolution also affects CPU use. Recording a 32 bit stream takes a lot more work than recording 16 bits.


How Many Bits To Use?

If there will be no adjustment of gain after recording and no effects applied, the recording bit depth can be the same or 1 bit more than the audio source bit depth without losing quality.


8 Bit

8 bit resolution is good for most recording of medium and low quality sources, such as:

  • Medium quality:
    • cassette
    • FM radio
  • Low quality:
    • AM radio
    • 78s
    • Microcassette
    • 8 track
    • Telephone audio
    • Reel to reel at 3.75ips or slower
    • Pocket recorders at live events

If medium quality sources are to be manipulated before saving the recording, it may be preferable to record in 16 bit to avoid any possible quality loss during application of effects. This does not apply to simple editing, and does not apply to low quality sources, whose resolution is below 8 bit.

Audacity 1.2 does not support 8 bit recording, 16 bit is the nearest option. It is possible to export projects in an 8 bit format.


16 Bit

16 bit matches audio CDs, and is thus suited where the better dynamic range and S/N ratio of CD quality audio is required. 16 bit is a good general purpose high quality setting. 16 bit recording is suitable for vinyl records.


24 Bit

24 bit recording may be used for signals that will be manipulated but still need to maintain the full 16 bit quality of CD audio. 24 bit is good for mastering.


32 Bit

32 bit recording is taking things to extremes. Although 32 bit recording can in theory have better technical specs than less bits, it is not often such great bit depth is needed. General purpose recording does not need 32 bit depth for the same reason clothing sizes do not come in increments of 1/1000th of an inch.

Finding audio sources capable of providing signals with better dynamic range than than 24 bit resolution is a demanding task. A 32 bit data stream records 65,000 times the dynamic range of 16 bit CD audio. In real world apps, a lot of those bits will be normally recording nothing but very low level background noise.

If you operate a recording studio and expect to do a large amount of manipulation of the data before mix down, and have audio source equipment with extremely low noise floor, 32 bit recording will give the best possible quality and avoid the bit depth having any effect on the sound even after heavy manipulation of the audio.

If you're just listening to thousands of pounds of expertly chosen high end audio kit, there is no reason to exceed 24 bit depth.


See Also