## Frequency band separation techniques

Scope and XITE Development

Original topic on PlanetZ: https://forums.scopeusers.com/viewtopic.php?t=24243

#### Frequency band separation techniques

Posted: Sat Jan 26, 2008 1:59 pm
by Shroomz~>
Hello,
I thought this subject might be an interesting one to discuss because there's more than one way to achieve band separation & it seems like the separation technique you choose would depend purely on the application (number of bands, device purpose etc). I've tried quite a few different methods now in the sdk which I'll detail if you like. I've had good results with all of them. I can see the benefits of certain methods for particular tasks, but thought it would be cool to discuss it & see what some of you guys think and have to offer on the subject. There's always the issue of cycle/memory cost as well, so that affects the method (module in the Scope paradigm) selection for particular tasks. What methods of band separation do you think are preferable & which do you prefer for given tasks? Ok, that's maybe a big question, but I think it's probably not & actually relatively simple for certain applications. Any thoughts? All input is welcome.

####

Posted: Sun Jan 27, 2008 1:08 pm
by MCCY
You know, that I'm a big fan of broad seperation like I did in most of my devices, but I'm not that smart concerning alternative methods & their advantages. I remember reading something with "fir" on it recently, but I might remember wrongly. As I'm no expert in digital filters I have no idea how to implement/build fir-filters... Is it possible with sdk?

####

Posted: Mon Jan 28, 2008 5:19 am
by tgstgs
'... Is it possible with sdk?'
YES;
back to the phase!?
_________
good vibes from vienna

####

Posted: Mon Jan 28, 2008 8:19 am
by hifiboom
I think there is even a fir atom in the sdk package....

####

Posted: Mon Jan 28, 2008 8:30 am
by MCCY
Sounds cool. Could anybody explain in easy words, what fir is, b.t.w.?
Or was "back on phase" a hidden hint once again? It's nicer to ask here than reading in wiki.

####

Posted: Mon Jan 28, 2008 11:47 am
by wolf
fir: finite impulse response filter, basically done with the delayed signal added to the original signal.
iir: infinite impulse response filter, basically done with a delay feeded back & added to the original signal.

####

Posted: Mon Jan 28, 2008 12:30 pm
by hifiboom

> MCCY wrote:Sounds cool. Could anybody explain in easy words, what fir is, b.t.w.?
> Or was "back on phase" a hidden hint once again? It's nicer to ask here than reading in wiki.

a lowpass is a mathematical technique to smoothen discrete values. quick discrete peaks are high freq. audio information.
fir uses a dedicated amount of delayed signals to calculate the new values.
iir uses the technique of recursive programming to calculate the new values.
mehr oder weniger sind alles mathematische Glättungsverfahren.
Glättung entspricht sozusagen einem Lowpass Filter.

####

Posted: Mon Jan 28, 2008 1:11 pm
by Shroomz~>
Hey, thanks for all the comments so far!

> MCCY wrote:You know, that I'm a big fan of broad seperation like I did in most of my devices

Yes, by broad separation I take it that you mean creating crossovers using configurations of HP & LP filters? Or maybe in a HP-BP-BP-LP setup?
You could also use a network of LP filters (6-24dB), sync inverters & 2>1 adders to create a nice separation circuit up to a certain No' of bands. It works on the theory that if you feed 2 LP filters with the same input signal, set one to say 300Hz & the other to say 3kHz then subtract the 300Hz filter output from the 3kHz filter ouput, you create a bandpass filter with a pass band of 300Hz - 3kHz.
I haven't tried the FIR approach though. Would that not be a bit much tax on the old dsps?
I guess there's alway's the parametric eq network as well, but I haven't investigated that as far up as 31 bands or anything like GRAPH EQ.

####

Posted: Mon Jan 28, 2008 3:02 pm
by Immanuel
When you using lp/hp/bp filters, remember that the filter frequency is the -3dB point. Therefor put to identically dialed filters in series for a good and easily usable -6dB point.

####

Posted: Mon Jan 28, 2008 10:20 pm
by tgstgs
@MCCY
its all about the phase you know . .
maybe now, with a 15 month delay,
you see my point in the funny phase discussion without emotion from a different phase position _;
---------
you can build your own filters or combine existing ones but dont invent the weel for a second time;
simple lowpass filter greetings
good vibes + (good vibes - 1sample) = cutofffrequency samplerate/2

####

Posted: Tue Jan 29, 2008 8:04 am
by hifiboom

> tgstgs wrote:
> good vibes + (good vibes - 1sample) = cutofffrequency samplerate/2

should be normalised to get the average value
goodvibes(t) / 2 + goodvibes(t-1) / 2 = cutofffrequency samplerate/2
so an add2N could be used in that case.

####

Posted: Tue Jan 29, 2008 9:24 am
by MCCY

> its all about the phase you know . .

Yeah. Spend hours on that topic.

> you can build your own filters or combine existing ones but dont invent the weel for a second time;

Now that was my point all the time, wasn't it? In the end all is about sound I'd say.
Fir seems to excede my knowledge for now (by far). From what I read here, in wiki & co. I'll have to learn quite a lot to understand those things on a more basic level... But I think best learning starts with interest

####

Posted: Wed Jan 30, 2008 3:05 pm
by tgstgs
@hifiboom
always sending full good vibes no half from vienna

####

Posted: Wed Jan 30, 2008 3:19 pm
by hifiboom
haha jeah,
my fault ! (nice one)

####

Posted: Thu Feb 07, 2008 11:39 pm
by sonolive
hi,

> '... Is it possible with sdk?'
> YES;

DONE !!! a fully new concept/algo of IIR ... 11 Eq modes ... SDK maths and +++
Screen shots and analysis coming soon ... Stay Tuned ...
cheers
olive

####

Posted: Fri Feb 08, 2008 1:32 am
by kylie

> sonolive wrote:Screen shots and analysis coming soon ... Stay Tuned ...

"soon" as in "scope5 coming soon" ?
nice to hear you have something new in preparation.
-greetings, markus-

#### the fir atom

Posted: Fri Feb 08, 2008 5:09 am
by alexmcmahon
The FIR atom is an enigma to me as is has no variables to configure - anyone know how to use it ? say to construct a FIR with 21 taps for example ?
Thanks

####

Posted: Fri Feb 08, 2008 5:21 am
by alexmcmahon
Another frequency band separation technique to consider is to use FFT, get rid of unwanted bands and do an IFFT

####

Posted: Fri Feb 08, 2008 1:57 pm
by Shroomz~>
Thanks for getting us back on topic Alexmcmahon.
You could also connect the LP & HP outputs of a multimode filter to a x-fade module, getting a new filter type which has a controllable curve. In the 0 x-fade position the new filter will be a notch or bandreject filter.

####

Posted: Sat Feb 09, 2008 7:23 pm
by Neutron
i bought an extra pulsar 1 with the explicit purpose of running crossover filters created on SDK to help design active crossovers and delays for amplifier-per-driver speakers.

####

Posted: Sun Feb 10, 2008 1:36 pm
by Shroomz~>

> <Shroomz> wrote:You could also connect the LP & HP outputs of a multimode filter to a x-fade module, getting a new filter type which has a controllable curve. In the 0 x-fade position the new filter will be a notch or bandreject filter.

Just to add to the comment above, the described method produces a notch filter which works well with zero or low resonance. To achieve a notch filter which works well at higher quality factors, try phase inverting the BP signal from your multimode filter & mixing it with the filter's input signal. This actually produces a notch filter which works well at both high & low quality factors.
Neutron, that sounds interesting.

####

Posted: Tue Feb 12, 2008 4:51 am
by sonolive
hi kylie,

> > sonolive wrote:
> > Screen shots and analysis coming soon ... Stay Tuned ...

> "soon" as in "scope5 coming soon" ?
> nice to hear you have something new in preparation.
> -greetings, markus-

as promised ...
https://forums.scopeusers.com/viewtopic.php?t=24380
cheers
olive