Brick wall schematic wanted!

[e96mlo]

Does anyone know where to find it? I've tried searching the web and this site without any results. I also would like to know how the phase of the filter is behaving.

/Marcus

[Havoc]

A brickwall is a theoretical concept. It means that it will pass everything up to a certain frequency and then without a transitionband, pass absolutely nothing. (or the inverse if a highpass) Its filter slope is infinitly steep. Its phase is perfect.

So the only things you will find are at best approximations. In general, the higher order filters with a steep slope have more phase deviation and ripple in the passband. Unless you go digital, but then you would not be on this part of the forum.

Why do you need it for? That way we could give you some ideas of what to look for and what to avoid.

[sangram]

Look for the filter design program on the TI website.

You'll be able to design 4-pole and 8-pole filters that will approximate a brickwall, and will also give you the phase response accross the frequency band. There was a link to the page on the forums, dang if I can find it. I have the file on my machine, but it's about 4 MB so I can't attach it here.

[rfbrw]

Search for elliptic filters.

ray.

[Fred Dieckmann]

I'll do even better than that!

http://doityourself.com/brick/retainingwall.htm

[e96mlo]

I thought that the filter used in the first generation of CD-players was called "brick wall" filters. But I think I got that wrong.

Anyway, I'm interested in the filters used in those early CD-players, since they had quite steep slopes etc.

Anyone got a link or two?

/Marcus

[Jiiim]

Dang!

Fred got there before me!

Nice to see a sense of humour round here once in a while.


Jim.

[Elso Kwak]

Hi e96mlo,
Links to the FilterPro lowpass filterdesign program can be found in this link. The program also gives a picture of the amplitude and the phase vs frequency.
CD square wave pre-ringing a filter problem?

A 8th order Chebyshev will be pretty close to a "brickwall" filter.
<B><I>Don't throw any bricks Fred!!!</B></I> (My avatar will protect me)

[peranders]

Originally posted by e96mlo
I thought that the filter used in the first generation of CD-players was called "brick wall" filters. But I think I got that wrong.

Anyway, I'm interested in the filters used in those early CD-players, since they had quite steep slopes etc.

Anyone got a link or two?

/Marcus

Hi!

My old Denon DCD-1000 had a 7th order LC-filter (20 kHz) and my other one DCD-1500 had a 9th order LC-filter at 35 kHz. Neither the DCD-1000 nor the DCD-1500 sounded very well. Was the LC-filters the cause? I don't know.

But what are going to use this filter for? It's much better to use a digital filter if it's possible.

[Tieftoener]

I don't know about a schematic that's already made for you - normally, you just have to pull out the 'ol TI-85 and make some calculations for some standard opamp filters. And because no design equation actually works in real life filter applications, you get to build it and test it.

But to make it easy on you, TI does have an application program for designing filters... not the greatest in my opinion though. Filter Wiz has a freeware version of their program and I like that much better than the TI program.

And to make it even easier... Linear Technology makes a variety of filter ICs already predesigned. The LTC1562 seems to have some good possibilities for an antialiasing filter or to rid your system of high frequency (above A-weighted values) noise in a post-DAC filter. My team looked into the LTC filters for our senior design project (DD, DPL, DTS, and stereo digital decoder) as additional antialiasing filters prior to our Burr Brown ADCs, but as it turns out the LTC filters are waaaaay to expensive for any realistic production cost. But for a DIYer, they're pretty fun to play with. And we really didn't need antialiasing filter because the BB ADC had one built in. I did some distortion analysis on Audio Precision with and without a modular filter I made with BB OPA2134 opamps, and it made no major improvement in distortion... so we just omitted the extra filter circuitry.

Hope this helps,