Digital filters needed

Archived from groups: rec.audio.pro (More info?)

Johann Burkard wrote:
> Hello,
>
> I'm looking for a digital filter (DirectX if possible) to remove
> narrowband high frequency noise. The noise peaks are only a couple of
> Hertz "wide" so Q must be really very very very very high.
>
> I've tried
>
> * Waves Q8 - frequency is not exact, Q not high enough
> * SoundForge Paragraphic EQ - Q not high enough
>
> Thanks for any recommendations.
>
> Johann
>
You may be confusing Q for notch depth. You do not NEED the filter to
have a high Q. If the filter is deep, it will remove the NB tone. If
the Q is high, it will have less effect on the surrounding frequencies.
If the Q is too high, the tuning will be very critical. Are the noise
peaks also stable with frequency? I don't think a moderate Q will hurt
the sound much. What you really need is notch depth. N track studio
has an EQ with a nice notch filter that may work for you.


Mark

Archived from groups: rec.audio.pro (More info?)

Johann Burkard <johannburkard@nexgo.de> wrote:
>
>I'm looking for a digital filter (DirectX if possible) to remove
>narrowband high frequency noise. The noise peaks are only a couple of
>Hertz "wide" so Q must be really very very very very high.

Nahh, you can get away with a surprisingly wide filter without anybody
noticing it, at high frequencies. Even an old Little Dipper is pretty
transparent when you're notching above 6 KC. Any parametric should be
fine... you might see a big chunk out on an FFT plot, but I bet you
can't hear it.

If you can, well, it might be time to skip filtration and go the CEDAR
route.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

"Johann Burkard"<
>
> Well I have seven noise peaks to remove, from ~11100 Hz to ~16900 Hz.


** No you do not.

There are no such things as "noise peaks".

That must be your own invented term .

Answer my previous points - or admit you are yet another PITA troll.




........... Phil

Archived from groups: rec.audio.pro (More info?)

I know you won't like this answer, but it may be interesting to pass
this through an MP3 encoder or other perceptual encoder and see what it
does.

It may remove some of your tones because it thinks they are masked
anyway.

What level are these tones compared to the program?
Can you hear them?

Mark

Archived from groups: rec.audio.pro (More info?)

In article <32vs76F3s6k0bU1@individual.net> philallison@tpg.com.au writes:

> "Johann Burkard"<
> >
> > Well I have seven noise peaks to remove, from ~11100 Hz to ~16900 Hz.
>
>
> ** No you do not.
>
> There are no such things as "noise peaks".
>
> That must be your own invented term .

A commonly accepted definition of "noise" is anything coming out that
you didn't put in. Distortion also meets this criteria, and by many,
it's lumped in with "noise."

I would suggest, since the frequencies were well defiined, that the
original poster is seeing amplitude peaks at those frequencies when he
looks at a "spectrum analyzer" display in his DAW. Since he didn't put
them there in the first place (or so he thinks - we don't know that),
to him this is "noise" and they are definitely "peaks" so while it may
not be correct to call them "noise peaks" his description is clear.

> Answer my previous points - or admit you are yet another PITA troll.

No, a troll is someone who posts a message that knowingly will cause
controvery, often off topic of the forum or newsgroup. Like the one to
which I am responding.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

Archived from groups: rec.audio.pro (More info?)

Johann Burkard wrote:

> Scott Dorsey wrote:
> > Johann Burkard <johannburkard@nexgo.de> wrote:
> >>I'm looking for a digital filter (DirectX if possible) to remove
> >>narrowband high frequency noise.
>
> > Nahh, you can get away with a surprisingly wide filter without anybody
> > noticing it, at high frequencies.
>
> Well I have seven noise peaks to remove, from ~11100 Hz to ~16900 Hz.
> With all the not-so-narrow-filters, that's a lot of high frequency
> attenuation - and it's audible.
>
> > If you can, well, it might be time to skip filtration and go the CEDAR
> > route.
>
> I assume CEDAR has FFT filters? Maybe I could write something like that
> myself.

The code for such filters isn't terribly complicated - you'll find some good
sources online.

Getting the code to talk to your application would be the tricky bit imho.


Graham

Archived from groups: rec.audio.pro (More info?)

Mark wrote:
> The EQ can be set for band stop i.e. notch filter, and with the
> highest Q setting it can create a notch 10 kHz 20 dB deep with only 1
> to 2 dB loss at 9 kHz. (At least thats what the display shows, I
> didn't actually sweep it to verify that).

The problem is that I have at least seven of these frequencies that I
need to take out.

Johann
--
Millionen Menschen koennen dich nicht unterhalten, da muss erst Toennes
im From: stehen und schon erweist du dem Kollegium° die Ehre deiner
aktiven Niederkunft im Torfmoor°. Fragen?
(*Tönnes in <cj4inl$irg$05$1@news.t-online.com> )