[linux-audio-user] what is DC? [was Re: Analyzing ogg files]

[Eric Dantan Rzewnicki]

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$ 
> >