Difference between revisions of "Proposal DC Management"

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(detailed discussion page linked from GR for DC management)
 
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== '''Page linked from Feature Requests for more detailed discussion''' ==
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__NOTOC__
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{{Proposal_Header|This page is a proposal for automatically removing DC bias.  }}
  
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== Proposed Feature ==
  
'''Koz wrote:'''  I want to subtract a feature. I want Audacity to not pass DC. Ever.  
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The proposal is an option (defaulted to on) to apply a low frequency high-pass filter to all audio in Audacity so that DC offset is removed.
  
I've seen the analysis coating the blackboard of why you need audio to respond all the way down to DC, but I'm here to tell you that it causes far more problems than it cures. DC is not sound and never has been.
 
  
I had to do some audio production in the field without my Cool Edit license, so naturally I fired up my Audacity. I got as far as adding silent stretches to the production and couldn't do it. It turned out, quite a bit later, that my show had a significant DC level on it and the silence generator didn't. I'm not in the habit of looking for non-audio signals in my audio show. It was a nasty surprise and should not have happened.
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== Developer Backing ==
  
It could be argued that scientists use Audacity for its ability to manage data signals. Terrific. There can be a data version for those six people.
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* None so far.
  
  
'''Stevethefiddle wrote:'''  That is really something that your sound card should do (or rather, not do).
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== Use Cases ==
  
I guess it would be quite easy to implement by passing all new audio (recorded or imported) through a low frequency high pass filter, but there would (inevitably?) be some processing time overhead involved, so is it fair to impose this overhead on everyone just because some users have faulty hardware?
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* For most users of Audacity for audio processing:
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** DC offset is not audible (so may not be corrected by the user) but reduces headroom for subsequent processing 
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** Differences in DC offset cause unwanted clicks where audio is tacked together
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* It is suggested that where a waveform is inherently asymmetrical, such as in recordings of brass instruments, Audacity's DC removal method (making the average positive and negative sample values equal) may create an offset.
  
  
'''Koz wrote:'''  the number of times this comes up, I'm betting a lot of people have local offset problems and either just haven't complained about it, or don't realize it's broken. No, people, effects are not supposed to pop, thump, and click when you apply them.
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== Background ==
  
And audio programs are not supposed to pass out-of-band energy--either direction. I'm perfectly happy to have a preference where you can force Audacity to pass everything from DC to 100KHz, but it's not an audio editor in that case. Hewlett-Packard, Fluke, and other manufacturers call those signal generators and amplifiers, not audio products.
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See [https://manual.audacityteam.org/o/man/dc_offset.html DC offset].  
  
  
'''Waxcylinder wrote:'''  Perhaps it should be a Preferences setting - but if so, the default should definitely be "Do not pass DC".
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== Previous Feature Requests relating to this proposal ==
  
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Correct as at October 2012.
  
'''Gale Andrews wrote:''' I suspect from memory of responses made in the past we'd not want to get involved modifying the signal in this way, even if it were technically possible (and I don't know enough about this kind of thing to comment in detail)... I know it doesn't stop the loss of headroom occurring, but a Feature Request for automatic removal of DC offset after recording (rather than just as an option in Normalize) might have more chance of being implemented).
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'''Better management of DC offset:'''
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* Automatic removal of DC offset after recording (rather than just as an option in Normalize) (7 votes)
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* Audacity should block DC at source because of the problems it causes. DC is not sound, and passing DC should only be a fringe purpose for scientists/researchers. (2 votes)  
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[[Category:Feature Planning]]

Latest revision as of 12:56, 21 August 2017

Proposal pages help us get from feature requests into actual plans. This page is a proposal for automatically removing DC bias.
Proposal pages are used on an ongoing basis by the Audacity development team and are open to edits from visitors to the wiki. They are a good way to get community feedback on a proposal.


  • Note: Proposals for Google Summer of Code projects are significantly different in structure, are submitted via Google's web app and may or may not have a corresponding proposal page.

Proposed Feature

The proposal is an option (defaulted to on) to apply a low frequency high-pass filter to all audio in Audacity so that DC offset is removed.


Developer Backing

  • None so far.


Use Cases

  • For most users of Audacity for audio processing:
    • DC offset is not audible (so may not be corrected by the user) but reduces headroom for subsequent processing
    • Differences in DC offset cause unwanted clicks where audio is tacked together
  • It is suggested that where a waveform is inherently asymmetrical, such as in recordings of brass instruments, Audacity's DC removal method (making the average positive and negative sample values equal) may create an offset.


Background

See DC offset.


Previous Feature Requests relating to this proposal

Correct as at October 2012.

Better management of DC offset:

  • Automatic removal of DC offset after recording (rather than just as an option in Normalize) (7 votes)
  • Audacity should block DC at source because of the problems it causes. DC is not sound, and passing DC should only be a fringe purpose for scientists/researchers. (2 votes)