need hardware platform for digital audio filter

[Andy]

Dear all,

is there a DSP hardware solution to the following problem:

take a mono audio signal, convert to digital,
perform a bandpass filter operation in real time, based on IIR
polynomial design,
filter order up to ten,
coefficients stored in ROM,
possibly some sort of user interface to change filter dynamically,
sampling frequency needs to be no more than about 1000 Hz
(low audio frequency application), 16 bit resolution,
convert back to analog,

i.e. basically a standalone fully custom bandpass audio filter with
parametric coefficients.

The code for this DSP module can probably be generated with software,
e.g. http://www.hitech.se/development/products/qedesign.htm

What's your advice?

Andy

 

[Ban]

Dear all,

is there a DSP hardware solution to the following problem:

take a mono audio signal, convert to digital,
perform a bandpass filter operation in real time, based on IIR
polynomial design,
filter order up to ten,
coefficients stored in ROM,
possibly some sort of user interface to change filter dynamically,
sampling frequency needs to be no more than about 1000 Hz
(low audio frequency application), 16 bit resolution,
convert back to analog,

i.e. basically a standalone fully custom bandpass audio filter with
parametric coefficients.

The code for this DSP module can probably be generated with software,
e.g. http://www.hitech.se/development/products/qedesign.htm

What's your advice?

Andy

Andy,
that sounds to me rather like a parametric bandpass filter which can be
implemented analogically. You can vary frequency, Q and gain/loss, the
delay(now latency) is minimal and there are beautiful knobs to play with.
There used to be a very good design (neteq) on the porteraudio web site but
it seems to exist no more. Luckily I have it stored on HD.

I think if you want to go digital you should have a look at Analog Devices
Shark Eval-boards, the ADSP-21161N or the 21261N which is the latest model.
There are libraries and example code available. The eval-kit has all you
need on board.
For your purposes you can also do that with an older PC and Cool Edit to see
if the results meet your exspectations. Or maybe with Matlab first.

good luck and ciao
Ban

 

[John Jardine]

Dear all,

is there a DSP hardware solution to the following problem:

take a mono audio signal, convert to digital,
perform a bandpass filter operation in real time, based on IIR
polynomial design,
filter order up to ten,
coefficients stored in ROM,
possibly some sort of user interface to change filter dynamically,
sampling frequency needs to be no more than about 1000 Hz
(low audio frequency application), 16 bit resolution,
convert back to analog,

i.e. basically a standalone fully custom bandpass audio filter with
parametric coefficients.

The code for this DSP module can probably be generated with software,
e.g. http://www.hitech.se/development/products/qedesign.htm

What's your advice?

Andy

http://www.alesis-semi.com/products.htm

Their integrated (and inexpensive) DSP chips are made for audio
applications.
john

 

[Andreas Moser]

http://www.alesis-semi.com/products.htm

Their integrated (and inexpensive) DSP chips are made for audio
applications.

I've got an old Alesis Microverb II and ideally that's what I would like
the filter module to look like. Is it feasible to design a board from
scratch though? If there were some sort of universal Alesis board where you
just plug in your own filter software, that would be perfect...

Andy

 

[Winfield Hill]

Ban wrote...

is there a DSP hardware solution to the following problem:
[ snip ] i.e. basically a standalone fully custom bandpass
audio filter with parametric coefficients. The code for
this DSP module can probably be generated with software,
e.g. http://www.hitech.se/development/products/qedesign.htm

That sounds to me rather like a parametric bandpass filter which can be
implemented analogically. You can vary frequency, Q and gain/loss, the
delay(now latency) is minimal and there are beautiful knobs to play with.
There used to be a very good design (neteq) on the porteraudio web site
but it seems to exist no more. Luckily I have it stored on HD.

That's an analog opamp filter you're referring to?

I think if you want to go digital you should have a look at Analog Devices
Shark Eval-boards, the ADSP-21161N or the 21261N which is the latest model.
There are libraries and example code available. The eval-kit has all you
need on board.
For your purposes you can also do that with an older PC and Cool Edit to
see if the results meet your exspectations. Or maybe with Matlab first.

Hmm, ADSP-21161N, with its impossible 225-ball MBGA package! What about
a less powerful floating-point DSP like the ADSP-21065L, available in a
slightly-more manageable 208-Lead 0.5mm-spacing Quad Flat Package [MQFP]?
Plus the ADDS-21065L-EZLITE development eval kit is $299 instead of $495.
Is there something suitable from AD that's even more simple - why do we
need all these leads and complexity anyway, for such a simple task? :>)

Thanks,
- Win

 

[Tim Shoppa]

Dear all,

is there a DSP hardware solution to the following problem:

take a mono audio signal, convert to digital,
perform a bandpass filter operation in real time, based on IIR
polynomial design,
filter order up to ten,
coefficients stored in ROM,
possibly some sort of user interface to change filter dynamically,
sampling frequency needs to be no more than about 1000 Hz
(low audio frequency application), 16 bit resolution,
convert back to analog,

With the sampling frequency for that low, a DSP is overkill. Any small
microprocessor can handle that rate.

I don't know of any small microcontroller with on-chip 16-bit A/D, though
adding one outboard won't be a big deal.

If your sampling rate were in the hundreds of kHz then it would be time
to think about DSPing.

Tim.

 

[Ban]

That's an analog opamp filter you're referring to?

I posted the files on ABSE. The individual filters can be cascaded

I think if you want to go digital you should have a look at Analog
Devices Shark Eval-boards, the ADSP-21161N or the 21261N which is
the latest model. There are libraries and example code available.
The eval-kit has all you need on board.
For your purposes you can also do that with an older PC and Cool
Edit to see if the results meet your exspectations. Or maybe with
Matlab first.

Hmm, ADSP-21161N, with its impossible 225-ball MBGA package! What
about a less powerful floating-point DSP like the ADSP-21065L,
available in a slightly-more manageable 208-Lead 0.5mm-spacing Quad
Flat Package [MQFP]? Plus the ADDS-21065L-EZLITE development eval
kit is $299 instead of $495. Is there something suitable from AD
that's even more simple - why do we need all these leads and
complexity anyway, for such a simple task? :>)

Thanks,
- Win

I think when you buy an evaluation board the chips don't matter much... the
big surprise is anyway that the software works only on that particular eval
board. When you design something custom, a very expensive software has to be
brought! But I do not think you will need a tenth order bandpass anyway. It
will be so slow reacting...

Try it with CoolEdit first. There are "scientific filters", which are
minimum phase IIR filters and reflect very well what you are desiring.

Surely a pic might do the job, but with over- and downsampling +
noise-shaping etc. you can get a 16-bit resolution even with only a 12bit
A/D.

If you just experiment, you nevertheless should go ADSP21161N with Stereo_in
and 6 outputs, that can be used in many more setups. Angelo Farina uses
these eval_boards in his Audio-DSP-classes(University of Parma) and is very
contented with them. Each student can write code and implement it
immediately. http://www.angelofarina.it/home.htm

ciao Ban

 

[Robert Lacoste]

Why not using a configurable analog bandpass filter, for example using a
Anadigm chip (www.anadigm.com I guess) ? I've experimented with these, and
with only one chip you can easily implement a 4-pole butterworth band pass
filter. For example I successfully built and checked a filter with the
following specs :
- 9.95 to 10.05KHz bandpass with less than 0.1dB ripple
- 30dB attenuation for F<9.3KHz and for F>10.8KHz.

Not too bad for a single chip solution, and easily configurable through
software, no ?

Cheers,

Robert Lacoste - ALCIOM : The mixed signals experts
http://www.alciom.com

 

[Ban]

I think if you want to go digital you should have a look at Analog
Devices Shark Eval-boards, the ADSP-21161N or the 21261N which is
the latest model. There are libraries and example code available.
The eval-kit has all you need on board.
For your purposes you can also do that with an older PC and Cool
Edit to see if the results meet your exspectations. Or maybe with
Matlab first.

Hmm, ADSP-21161N, with its impossible 225-ball MBGA package! What
about a less powerful floating-point DSP like the ADSP-21065L,
available in a slightly-more manageable 208-Lead 0.5mm-spacing Quad
Flat Package [MQFP]? Plus the ADDS-21065L-EZLITE development eval
kit is $299 instead of $495. Is there something suitable from AD
that's even more simple - why do we need all these leads and
complexity anyway, for such a simple task? :>)

Thanks,
- Win

I think when you buy an evaluation board the chips don't matter
much... the big surprise is anyway that the software works only on
that particular eval board. When you design something custom, a very
expensive software has to be brought!

My interest is in putting the DSP filters in small instruments.
How much does Analog charge for the unlimited-use compilers?

Visual DSP++ full 3745$, and an USB Emulator 4280$

Yes, he's doing serious stuff. I have in mind relatively simple
filters, and need to be able to hand-make the pc boards in small
quantitites. Older chips like the 208-lead MQFP ADSP-21065L can
be hand assembled (barely), but then one wonders if are they all
going to be discontinued?

Thanks,
- Win

The development software has to be bought for each family of processors
again, so it doesn't make sense to get an older model (exept on EBay). The
EZkit lite software is crippled and works only with this particularly
numbered chip. The number is stored inside the boot sector of the processor
I think.
All manufacturers have a similar system selling their software, and the
prices are in the same range. And even if most DSP-chips seem to be very
good priced this will limit their use strictly to professional markets.

ciao Ban