Ah sorry I missed that. Yes, pretty much the same. And this has to be
minimal-phase although there's no attempt to make it so. And no, this is no
linear phase BUT if the moving average filter has low sidelobes then it is
ALMOST linear phase in audible range, because there's hardly any subtraction
there. This applies to FIR as well as IIR filters as long as the DC-blocking
is constructed by subtraction. If the moving average is FIR then the whole
DC-blocking is FIR; if that is IIR then so is this. Regarding
linear-phaseness their outcomes are the same in audio range, as long as the
moving average output is kept below.
Xue
-----Original Message-----
From: Domagoj Saric
Sent: Wednesday, August 01, 2012 9:39 AM
To: music-dsp@music.columbia.edu
Subject: Re: [music-dsp] DC blocking (again :)
On 31.7.2012. 12:54, Wen Xue wrote:
5ms moving-average doesn't sound very right for it cuts off anything below
200Hz, no matter how much one upsamples it. However it is probably "just
fine"
to subtract a DC measured 500ms ago from the current waveform because the
DC
shouldn't change much in that time or it can't be DC. This subtraction you
can
write as a anti-DC filter which is FIR with a big delay on the unwanted
part but
no delay on the wanted part. There might be some DC left - but probably
significantly suppressed - depending on how DC-ish it is.
Is this the same/similar to what I mentioned in the first post:
<<
Then there is the modification
(http://www.dsprelated.com/showmessage/80739/2.php, Andor's post) to
subtract
the moving average from the _current_ sample (instead of the one
corresponding
to the middle of the moving average filter) but this supposedly makes the
filter
minimal-phase instead of linear-phase so it is still a no go (at least
AFAICT
from my limited knowledge).
?
--
Domagoj Saric
Software Architect
www.LittleEndian.com
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