DSP LPF with zero phase-shift, & filter design software. - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th August 2002, 01:44 PM   #1
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
Default DSP LPF with zero phase-shift, & filter design software.

Hi all.
What I need is at least a 10th order 20kHz zero phase-shift LPF. The reason I need zero phase shift is that I want to put it in the forward path of an amplifier to roll off the response well before the inherent phase shift at high frequencies of the other stages of the amplifier start to kick in. This way I can (maybe) apply a big heap of negative feedback around the whole amp without such a great risk of HF instability because the amplifier gain has dropped to unity or less at HF by our little filter.

Now I reveal how lazy I am ;-) Is there some software that will enable me to specify the filter parameters I want e.g corner frequency, slope etc just by pushing a few buttons, and will generate some suitable ready-to-run code that can then be burnt? Is there a chip that has both 16 bit A/D & D/A for this application?

I looked at the TI website but was just overwhelmed by the volume of stuff :-( Everything I have looked at so far assumes you are already a rocket scientist, but in this case I don't yet at least want to learn all the in's and out's of DSP, just make a filter so I can get on with my project.

TIA G.P.
  Reply With Quote
Old 4th August 2002, 02:42 PM   #2
tiroth is offline tiroth  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Check out Alesis semiconductor's AL3101. It is far from a turnkey solution, but it is easily interfaced and addressed. There is even a cheap ($200?) demo board to play with.

The main limitation is 48kHz sample rate.
  Reply With Quote
Old 4th August 2002, 02:53 PM   #3
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default DSP etc

Hi Circlotron,

You may want to take a look at the 2-channel DSP filter which was described recently in EW. It is 2-channel, consisting of a pair of ADC and DAC'S with standard CD quality, interfacing to a DSP. Nice thing is that there is Windows software to spec the filter characteristics and download them to the card. This may not be the solution to put in your amps, but it is very versatile (IRR/FIR with up to 1024 taps!) that you could use it for testing. Not really cheap, I think some US $ 600.
Unfortunately, I cannot give you the ref right now, will have to wait until tomorrow afternoon. Sorry. But maybe you already know about it?

Cheers, Jan Didden
  Reply With Quote
Old 4th August 2002, 04:24 PM   #4
diyAudio Member
 
Join Date: Jan 2001
Location: Scandinavia
Digital filters imply delay. Delay is basically the same as phase shift. I would be weary of this approach.

BTW DAC chips often have digital filters built in. If you want a separate unit, consider looking at the TI PCM1704 datasheet where an external digital filter is referenced. Other manufacturers make such filters as well.

Petter
  Reply With Quote
Old 4th August 2002, 07:40 PM   #5
mirlo is offline mirlo  United States
diyAudio Member
 
Join Date: Jul 2002
Location: San Diego
Default Rocket science

I too would be wary of this approach. A high order LPF has a lot of delay, even if it is "linear phase" (which means it has only delay as its phase response), and you will have "fun" making something stable.

But perhaps there is another similar approach that would give the results you want. If you let the DSP have two inputs, one is the input signal and one is the feedback signal from the amplifier output, you might get somewhere.

However, I think that to do this well, you will need to learn some of that rocket science. Control theory really IS rocket science.

I'm not sure of a good cookbook type reference, because what you want to do is digital control, not just digital signal processing, so you would need to use aspects of both control theory and DSP to get it right, and you would presumably have to model the response of the amplifier to design the compensator for it.

Good books on Rocket Science are unfortunately rather expensive. Oppenheim and Schafer have a good one called Discrete Time Signal Processing. There is a book called something like Digital Control of Dynamic Systems by Franklin, Powell, and Workman.

Maybe you can find some more cookbook type references by browsing Amazon starting with those books, and looking at the lists and "people who bought this also bought ..." links.

Also look at this one: http://www.dspguru.com/info/faqs/firfaq.htm

Have fun,

-- mirlo
  Reply With Quote
Old 5th August 2002, 07:18 PM   #6
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default DSP LPF etc

Circlotron,

The reference I promised is a real-time digital filter on www.umist.ac.uk/dias/pag/signalwizard.htm.
In view of the above you may already have changed your mind. BUT, the signalwizard is dual channel so it might still work with parallel paths as described above. Proce is steep though at UKP 499.

Jan Didden
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
phase shift of second order filter bondo Multi-Way 9 8th April 2009 03:24 AM
Active filter design software lochness Tubes / Valves 25 11th July 2008 01:04 AM
design software for active filter dick van nierop Chip Amps 7 20th March 2006 05:25 PM
FilterLab® Active Filter Design Software peranders Everything Else 0 24th March 2004 12:33 PM


New To Site? Need Help?

All times are GMT. The time now is 03:03 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2