Subject: Re: [linux-audio-user] what is DC? [was Re: Analyzing ogg files]
From: Eric Dantan Rzewnicki (rzewnickie_AT_rfa.org)
Date: Wed Dec 03 2003 - 19:48:36 EET
Thank you Reuben.
-Eric Rz.
On Wed, Dec 03, 2003 at 11:23:50AM -0600, Reuben Martin wrote:
> DC offset is when there is a Direct Current running over the same lines that audio runs through. Since sound signals are a type of Alternating Current, the addition of the DC tends to shift, or offset, the audio signal.
>
> regards
> -Reuben
>
> -----Original Message-----
> From: Eric Dantan Rzewnicki [mailto:rzewnickie_AT_rfa.org]
> Sent: Wednesday, December 03, 2003 11:10 AM
> To: A list for linux audio users
> Subject: [linux-audio-user] what is DC? [was Re: Analyzing ogg files]
>
>
> What is DC offset in this context? I've seen this term on this list
> before, but don't really understand what it means.
>
> Is this the same thing refered to by the ecasound options -ezf and -ezx?
>
> -ezf
> Finds the optimal value for DC-adjusting. You can use the result as
> a parameter to -ezx effect.
>
> -ezx:channel-count,delta-ch1,...,delta-chN
> Adjusts the signal DC by 'delta-chX', where X is the channel number.
> Use -ezf to find the optimal delta values.
>
> or is that a different DC?
>
> -Eric Rz.
>
> On Tue, Dec 02, 2003 at 07:38:54PM -0800, Mark Knecht wrote:
> > On Tue, 2003-12-02 at 13:06, Andrew Burgess wrote:
> > > >> Is there a DC offset which the cheap card is eating?
> > >
> > > >A DC offset is an interesting idea. How would I test for that?
> > >
> > > sox <file> -e stat
> > >
> > > displays midline amplitude.
> > >
> > > Or try a highpass filter, just as a test.
> > >
> >
> > More data, but I'm not sure there's an answer there yet. The first file
> > creates a very loud glitch sound, which the second one doesn't. The
> > midline value seems better on the first, assuming this represents DC
> > offset.
> >
> > bash-2.05b$ sox gmc2.ogg -e stat
> > Samples read: 26972160
> > Length (seconds): 305.806803
> > Scaled by: 2147483647.0
> > Maximum amplitude: 0.999969
> > Minimum amplitude: -1.000000
> > Midline amplitude: -0.000015
> > Mean norm: 0.138033
> > Mean amplitude: 0.000003
> > RMS amplitude: 0.189967
> > Maximum delta: 0.959961
> > Minimum delta: 0.000000
> > Mean delta: 0.093997
> > RMS delta: 0.128996
> > Rough frequency: 4766
> > Volume adjustment: 1.000
> >
> > bash-2.05b$ sox examplesustain.ogg -e stat
> > Samples read: 11361130
> > Length (seconds): 128.810998
> > Scaled by: 2147483647.0
> > Maximum amplitude: 0.649841
> > Minimum amplitude: -0.661896
> > Midline amplitude: -0.006027
> > Mean norm: 0.069344
> > Mean amplitude: 0.002177
> > RMS amplitude: 0.092420
> > Maximum delta: 0.784546
> > Minimum delta: 0.000000
> > Mean delta: 0.072115
> > RMS delta: 0.095279
> > Rough frequency: 7235
> > Volume adjustment: 1.511
> > bash-2.05b$
> >
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