Subject: RE: [linux-audio-user] what is DC? [was Re: Analyzing ogg files]
From: Reuben Martin (MartinR_AT_jbu.edu)
Date: Wed Dec 03 2003 - 19:23:50 EET
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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