[audacity4blind] Re: Reducing hum with audacity.
- From: "David R. Sky" <davidsky@xxxxxxxxxxxxxx>
- To: audacity4blind@xxxxxxxxxxxxx
- Date: Mon, 26 Jun 2006 22:25:24 -0700 (PDT)
Hi Anders,
To remove one specific frequency, don't use the lowpass or highpass
filters, use the notch filter I've attached, called notch50.ny - the
default frequency it will remove is fifty hertz.
Three edit fields: remove 60hz, remove 50hz, or remove frequency of your
choice. Default is remove 50hz.
Next edit field: if you've chosen to remove another frequency, enter it
into this field.
Third edit field: what's known as 'q' or 'quality' of filtering. A lower
value removes a wider range of frequencies centered around the notch
frequency you chose.
David
On Tue, 27 Jun 2006, Anders Holmberg wrote:
Hello!
I am about to reduce hom or try to remove it with audacity.
Its from a radio show which i recorded from my stereo receiver.
I didn't realize there was a grounding problem.
Its a 50HZ hum which is really annoying to listen to.
Can anybody here recomend which filter i should use to reduce this hum?
And which cutoff frequency would be the best to use?
I have tried to use lowpass filter from 40 hz and highpass filter from 70 hz.
But i am no mathematics which now seem to be abit frustrating to me.
I am no good in counting so i hope someone can clear out this for me.
Sorry.
Thanks in advance.
/Anders.
;nyquist plug-in
;version 1
;type process
;name "Notch Filter..."
;action "Applying Notch Filter..."
;info "by David R. Sky\nReleased under terms of GNU Public License\nlower q
gives wider notch"
;control choice "Default choice" int "0=60 1=50 2=variable" 1 0 2
;control freq "Notch frequency" real "Hz" 60.0 20.0 20000.0
;control q "Notch q" real "Q" 1.00 0.01 5.00
; Notch filter by David R. Sky
; updated January 2, 2006
; Released under terms of the GNU Public License
; http://www.opensource.org/licenses/gpl-license.php
(setf freq (cond
; remove 60 Hz hum, North America
((= choice 0) 60)
; remove 50Hz hum, UK and elsewhere
((= choice 1) 50)
; set other desired notch frequency
((= choice 2) freq)))
; if audio is stereo...
(if (arrayp s)
; apply notch to stereo audio
(vector (notch2 (aref s 0) freq q)
(notch2 (aref s 1) freq q))
; ... otherwise apply to mono
(notch2 s freq q))
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