| Author |
Message |
Bjarni Juliusson
Guest
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 Posted:
Mon Nov 22, 2004 10:05 pm Post subject:
Analog filter |
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I don't know if this is the right place to ask, but there seemed to be a
fair amount of activity in this group, so at least someone might be able
to point me in the right direction.
I want to build an analog audio filter, and I have never done anything
like it before. It needs to be controlled by a digital device, so I also
need some advice on how to do that (that is, say the cutoff is
represented by a 16 bit binary number and needs to be converted to an
analog signal of some sort). I'd like to build high, low and bandpass
filters, of decent quality but not too complicated. Any pointers
appreciated. I am an almost complete beginner in audio electronics.
Bjarni
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Per Stromgren
Guest
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| Posted:
Mon Nov 22, 2004 10:05 pm Post subject:
Re: Analog filter |
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On Mon, 22 Nov 2004 22:08:52 +0100, Bjarni Juliusson
<bjarni.ferret@update.ferret.uu.se> wrote:
| Quote: | I don't know if this is the right place to ask, but there seemed to be a
fair amount of activity in this group, so at least someone might be able
to point me in the right direction.
|
I'm sure we can help you here.
| Quote: |
I want to build an analog audio filter, and I have never done anything
like it before. It needs to be controlled by a digital device, so I also
need some advice on how to do that (that is, say the cutoff is
represented by a 16 bit binary number and needs to be converted to an
analog signal of some sort). I'd like to build high, low and bandpass
filters, of decent quality but not too complicated. Any pointers
appreciated. I am an almost complete beginner in audio electronics.
|
Then this does not seem to be the right place to start, if you ask me.
However, if you tell us the application for your filter, we may be of
a lot more help! Will this filter be operating in the analog domain,
completely? At line level or something else? Why do you want to build
it yourself instead of buying a commercial product?
Per. |
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Bjarni Juliusson
Guest
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| Posted:
Tue Nov 23, 2004 6:07 pm Post subject:
Re: Analog filter |
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Per Stromgren wrote:
| Quote: | On Mon, 22 Nov 2004 22:08:52 +0100, Bjarni Juliusson
bjarni.ferret@update.ferret.uu.se> wrote:
I don't know if this is the right place to ask, but there seemed to be a
fair amount of activity in this group, so at least someone might be able
to point me in the right direction.
I'm sure we can help you here.
|
Utmärkt :-)
| Quote: | I want to build an analog audio filter, and I have never done anything
like it before. It needs to be controlled by a digital device, so I also
need some advice on how to do that (that is, say the cutoff is
represented by a 16 bit binary number and needs to be converted to an
analog signal of some sort). I'd like to build high, low and bandpass
filters, of decent quality but not too complicated. Any pointers
appreciated. I am an almost complete beginner in audio electronics.
Then this does not seem to be the right place to start, if you ask me.
However, if you tell us the application for your filter, we may be of
a lot more help!
|
General music filtering, for timbre effects. I'm a computer guy, both
hardware and software, and now I'd like to experiment with audio
synthesis. For that reason, I'd like to look into how one builds a
fairly simple filter. Any hints are welcome. I know very little of
analog electronics, and I want to learn.
| Quote: | Will this filter be operating in the analog domain,
completely?
|
What do you mean by that? The filter should be a simple analog device,
taking analog inputs and producing analog output. The digital parts are
only for a computer to be able to generate the analog controls.
| Quote: | At line level or something else?
|
If that is the particular voltage range used for "line out" as found in
typical household audio equipment, then yes, that would be nice. What is
the actual voltage? Did I mention I'm a beginner?
| Quote: | Why do you want to build
it yourself instead of buying a commercial product?
|
Building it yourself is more fun, and more educational.
Bjarni |
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Per Stromgren
Guest
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| Posted:
Tue Nov 23, 2004 10:03 pm Post subject:
Re: Analog filter |
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On Tue, 23 Nov 2004 18:38:06 +0100, Bjarni Juliusson
<bjarni@update.uu.se> wrote:
| Quote: |
General music filtering, for timbre effects. I'm a computer guy, both
hardware and software, and now I'd like to experiment with audio
synthesis. For that reason, I'd like to look into how one builds a
fairly simple filter. Any hints are welcome. I know very little of
analog electronics, and I want to learn.
|
You *could* do this with analog filters, it was always done this way,
but the common technology today is of course to do all filtering in
the digital domain. Digital filters can do everything analog filters
can, and a lot they can't.
In both the analog and digital filter design you start with a
transmision function, based on what you want to do. Then you implement
this filter with analog devices or does it in software. Software is so
much easier, nowadays. There where a time (in the dark ages when I was
a young EE engineer in the early 70's) when this was expensive and not
so easy, but now the cheapest cell phone has more digital filtering
that you thought you needed...
| Quote: |
Will this filter be operating in the analog domain,
completely?
What do you mean by that? The filter should be a simple analog device,
|
Well, it can't be *that* simple if you want to control it from your
software.
| Quote: | taking analog inputs and producing analog output. The digital parts are
only for a computer to be able to generate the analog controls.
At line level or something else?
If that is the particular voltage range used for "line out" as found in
typical household audio equipment, then yes, that would be nice.
|
OK
| Quote: | What is
the actual voltage?
|
Around 1 volt.
| Quote: | Did I mention I'm a beginner?
|
Yes, I realize that.
| Quote: |
Why do you want to build
it yourself instead of buying a commercial product?
Building it yourself is more fun, and more educational.
|
OK. Perhaps you should start building the filters without the software
control, in order to learn how they work? If I interpret your e-mail
address correctly, there should be plenty information at the EE
department of your university!
But I still think you should do your filter experiments in software,
it's right there at your fingertips!
Introduktion to digital filters:
http://www.dsptutor.freeuk.com/dfilt1.htm
Per,
EE from KTH |
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Bjarni Juliusson
Guest
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| Posted:
Wed Nov 24, 2004 10:06 pm Post subject:
Re: Analog filter |
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Per Stromgren wrote:
| Quote: | On Tue, 23 Nov 2004 18:38:06 +0100, Bjarni Juliusson
bjarni@update.uu.se> wrote:
General music filtering, for timbre effects. I'm a computer guy, both
hardware and software, and now I'd like to experiment with audio
synthesis. For that reason, I'd like to look into how one builds a
fairly simple filter. Any hints are welcome. I know very little of
analog electronics, and I want to learn.
You *could* do this with analog filters, it was always done this way,
but the common technology today is of course to do all filtering in
the digital domain. Digital filters can do everything analog filters
can, and a lot they can't.
|
....which is a typical news answer it seems. But it doesn't answer the
question. I want to make it clear that I'm not really interested in
getting optimal sound quality or learning the math or learning how to
program. See below.
| Quote: | Will this filter be operating in the analog domain,
completely?
What do you mean by that? The filter should be a simple analog device,
Well, it can't be *that* simple if you want to control it from your
software.
|
That interface should hardly complicate matters much. The filter itself
is the same, and the interface points ough to be pretty much vanilla
circuitry. Besides, when I say "simple", I don't mean two transistors
simple; I'm prepared to build a somewhat more complicated circuit than
that :-).
| Quote: | What is the actual voltage?
Around 1 volt.
|
OK. Thanks.
| Quote: | OK. Perhaps you should start building the filters without the software
control, in order to learn how they work?
|
Well sure, I could do that. Do you have any knowledge that will help me
to build it, or should I look elsewhere?
| Quote: | If I interpret your e-mail
address correctly, there should be plenty information at the EE
department of your university!
|
That is one place I could look, but I thought I'd ask here first because
it's less work and I figured I was more likely to get a good answer.
| Quote: | But I still think you should do your filter experiments in software,
it's right there at your fingertips!
|
Yes, but I had that much figured out by myself. Naturally I could do it
in software, but I'm not interested in that.
OK, thanks. The request remains however :-).
Bjarni |
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John Walton
Guest
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| Posted:
Thu Nov 25, 2004 2:08 pm Post subject:
Re: Analog filter |
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Both Analog Devices www.analog.com and Microchip Technology
www.microchip.com have application notes on the use of use of digital
potentiometers for filtration. The interface can be I2C, SPI, etc. Some of
the things you have to be mindful of are the noise and bandwidth of these
chips. TI also has a line of digital controls -- very high quality units.
Maxim Technology now owns Dallas Semiconductor - they have a line of digital
potentiometers which can be "manually controlled".
You don't have to bother working the transfer functions to design the
filters -- you can download Texas Instruments "Filter Pro" software from
their website -- it is a really wonderful tool. Analog also has an
interactive filter tool on their site, but I find it a little less
user-friendly.
Jack
"Bjarni Juliusson" <bjarni.ferret@update.ferret.uu.se> wrote in message
news:cntkh9$m0p$1@Tempo.Update.UU.SE...
| Quote: | I don't know if this is the right place to ask, but there seemed to be a
fair amount of activity in this group, so at least someone might be able
to point me in the right direction.
I want to build an analog audio filter, and I have never done anything
like it before. It needs to be controlled by a digital device, so I also
need some advice on how to do that (that is, say the cutoff is
represented by a 16 bit binary number and needs to be converted to an
analog signal of some sort). I'd like to build high, low and bandpass
filters, of decent quality but not too complicated. Any pointers
appreciated. I am an almost complete beginner in audio electronics.
Bjarni |
|
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| Back to top |
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Bjarni Juliusson
Guest
|
| Posted:
Thu Nov 25, 2004 5:57 pm Post subject:
Re: Analog filter |
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John Walton wrote:
| Quote: | Both Analog Devices www.analog.com and Microchip Technology
www.microchip.com have application notes on the use of use of digital
potentiometers for filtration. The interface can be I2C, SPI, etc. Some of
the things you have to be mindful of are the noise and bandwidth of these
chips. TI also has a line of digital controls -- very high quality units.
|
Now that sounds like something I could use. I will have a look.
| Quote: | You don't have to bother working the transfer functions to design the
filters -- you can download Texas Instruments "Filter Pro" software from
their website -- it is a really wonderful tool. Analog also has an
interactive filter tool on their site, but I find it a little less
user-friendly.
|
Cool, I will check them out.
Thanks for your help!
Bjarni |
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Per Stromgren
Guest
|
| Posted:
Thu Nov 25, 2004 10:12 pm Post subject:
Re: Analog filter |
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On Wed, 24 Nov 2004 21:46:44 +0100, Bjarni Juliusson
<bjarni@update.uu.se> wrote:
| Quote: |
...which is a typical news answer it seems. But it doesn't answer the
question. I want to make it clear that I'm not really interested in
getting optimal sound quality or learning the math or learning how to
program. See below.
|
So you are interested in exactly what? Designing analog filters?
Building boxes that sound hip? Impressing your girl friends? :-)
No, seriously, if your interest is in the filter design itself, you
can play with this without pulling out you soldering iron. In fact,
you do all your design on paper, it's pure math, nothing else. You
*have* to learn the math, if you want to learn anything in this part
of science! The theory behind all this was pretty much settled 60-70
years ago, with digital entering in the 60's. The telecoms industry
knows everything about, be it analog or digital.
If you want to listen to your filters, it is nice to know that they
will sound the same both in analog and digital design.
| Quote: |
That interface should hardly complicate matters much. The filter itself
is the same, and the interface points ough to be pretty much vanilla
circuitry. Besides, when I say "simple", I don't mean two transistors
simple; I'm prepared to build a somewhat more complicated circuit than
that :-).
|
Good. I saw another poster giving you pointers.
| Quote: |
Well sure, I could do that. Do you have any knowledge that will help me
to build it, or should I look elsewhere?
|
I have my old litterature from the university, of course, but your
university library is probably full of books on the matter.
| Quote: |
That is one place I could look, but I thought I'd ask here first because
it's less work and I figured I was more likely to get a good answer.
|
What? After reading my posts? :-) My prof would be proud...
Take my advice, go talk to them, they will gladly help an interested
student!
| Quote: |
But I still think you should do your filter experiments in software,
it's right there at your fingertips!
Yes, but I had that much figured out by myself. Naturally I could do it
in software, but I'm not interested in that.
|
Can't you tell us why?
Per. |
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Bjarni Juliusson
Guest
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| Posted:
Fri Nov 26, 2004 2:12 am Post subject:
Re: Analog filter |
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Per Stromgren wrote:
| Quote: | On Wed, 24 Nov 2004 21:46:44 +0100, Bjarni Juliusson
bjarni@update.uu.se> wrote:
...which is a typical news answer it seems. But it doesn't answer the
question. I want to make it clear that I'm not really interested in
getting optimal sound quality or learning the math or learning how to
program. See below.
So you are interested in exactly what? Designing analog filters?
Building boxes that sound hip? Impressing your girl friends? :-)
|
Playing. Not interested in being hip or impressing a hypothetical
girlfriend :-).
| Quote: | No, seriously, if your interest is in the filter design itself, you
can play with this without pulling out you soldering iron. In fact,
you do all your design on paper, it's pure math, nothing else. You
*have* to learn the math, if you want to learn anything in this part
of science! The theory behind all this was pretty much settled 60-70
years ago, with digital entering in the 60's. The telecoms industry
knows everything about, be it analog or digital.
|
Well, yes, but I'm not interested in *implementing* the filters in
software even if software can help in the design. It's playing with
analog electronics I'm interested in. I'll have to do some math to
design filters, but I don't want to learn about filters as a way to
learn lots of math.
| Quote: | If you want to listen to your filters, it is nice to know that they
will sound the same both in analog and digital design.
|
I know perfectly well that a computer at all approaching turing
completeness can be programmed to approximate an analog filter, but
that's not the kind of fun I'm looking for.
| Quote: | Well sure, I could do that. Do you have any knowledge that will help me
to build it, or should I look elsewhere?
I have my old litterature from the university, of course, but your
university library is probably full of books on the matter.
|
Quite possible. I can probably find some professor to point me in the
right direction not far from where I am sitting now. I'll go ask.
| Quote: | But I still think you should do your filter experiments in software,
it's right there at your fingertips!
Yes, but I had that much figured out by myself. Naturally I could do it
in software, but I'm not interested in that.
Can't you tell us why?
|
No, it's not an intellectual choice. It is an actual live example of
interest. Play with programming and math all days, and even digital
electronics; felt like playing with some analog electronics next.
Bjarni |
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Overdog
Guest
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| Posted:
Fri Nov 26, 2004 10:12 am Post subject:
Re: Analog filter |
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|
Bjarni Juliusson <bjarni@update.uu.se> wrote in message news:<co50uu$e7p$1@Tempo.Update.UU.SE>...
| Quote: | John Walton wrote:
Both Analog Devices www.analog.com and Microchip Technology
www.microchip.com have application notes on the use of use of digital
potentiometers for filtration. The interface can be I2C, SPI, etc. Some of
the things you have to be mindful of are the noise and bandwidth of these
chips. TI also has a line of digital controls -- very high quality units.
Now that sounds like something I could use. I will have a look.
You don't have to bother working the transfer functions to design the
filters -- you can download Texas Instruments "Filter Pro" software from
their website -- it is a really wonderful tool. Analog also has an
interactive filter tool on their site, but I find it a little less
user-friendly.
Cool, I will check them out.
Thanks for your help!
Bjarni
|
If you don't already have it, you should take a look at "The Art of
Electronics" by Horowitz & Hill. It's a pretty good electronics book,
designed for beginniners.
I think what you will find, though, is that unless you are some kind
of math genius, you will end up copying someone else's analog filter
design. Basically, the only work you will be doing is soldering.
Or you could just buy a single chip that does everything you need!
Overdog |
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Gareth Magennis
Guest
|
| Posted:
Fri Nov 26, 2004 3:34 pm Post subject:
Re: Analog filter |
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|
Try Googling for "DIY synth circuits". There are loads of people
experimenting like this and loads of diagrams and explanations too. There's
not much on the digital control side of things, but most of the circuits
you'll find are voltage controlled anyway.
For the digital side I suggest you read up on Programming Microcontrollers.
The 8051 family are powerful, cheap and well supported.
Gareth.
"Bjarni Juliusson" <bjarni.ferret@update.ferret.uu.se> wrote in message
news:cntkh9$m0p$1@Tempo.Update.UU.SE...
| Quote: | I don't know if this is the right place to ask, but there seemed to be a
fair amount of activity in this group, so at least someone might be able to
point me in the right direction.
I want to build an analog audio filter, and I have never done anything
like it before. It needs to be controlled by a digital device, so I also
need some advice on how to do that (that is, say the cutoff is represented
by a 16 bit binary number and needs to be converted to an analog signal of
some sort). I'd like to build high, low and bandpass filters, of decent
quality but not too complicated. Any pointers appreciated. I am an almost
complete beginner in audio electronics.
Bjarni |
|
|
| Back to top |
|
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Bjarni Juliusson
Guest
|
| Posted:
Sun Nov 28, 2004 12:09 am Post subject:
Re: Analog filter |
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|
Gareth Magennis wrote:
| Quote: | Try Googling for "DIY synth circuits". There are loads of people
experimenting like this and loads of diagrams and explanations too. There's
not much on the digital control side of things, but most of the circuits
you'll find are voltage controlled anyway.
|
Yes, I've been googling already. I think I'll just pick one of the
designs and try it out! Just as you say, I haven't found anything about
digital control, but that's important to me. How do I generate a voltage
digitally? Perhaps by a counter counting really fast and flipping a
flip-flop connected to a transistor that feeds a capacitor :-). Isn't
that how switching power supplies work? Anyway, there is naturally a
simpler way...
| Quote: | For the digital side I suggest you read up on Programming Microcontrollers.
The 8051 family are powerful, cheap and well supported.
|
Er, the 8051 has no analog outputs does it? Anyway, the digital side
isn't really a problem. I'm a computing science student and all that,
it's just the conversion of 16 bits of TTL into a voltage that I don't
know how to do.
Anyway, thanks everybody for your help! I got some pointers, and I think
I know what to do, except the digital->analog part; I'll go google.
Bjarni |
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Bjarni Juliusson
Guest
|
| Posted:
Sun Nov 28, 2004 12:09 am Post subject:
Re: Analog filter |
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Overdog wrote:
| Quote: | If you don't already have it, you should take a look at "The Art of
Electronics" by Horowitz & Hill. It's a pretty good electronics book,
designed for beginniners.
|
I will. Thanks.
| Quote: | I think what you will find, though, is that unless you are some kind
of math genius, you will end up copying someone else's analog filter
design. Basically, the only work you will be doing is soldering.
|
If I can find a design that fits my needs, that's fine for a start. I
don't mean that I won't learn the math, but I don't want to just write
some program to do the filtering - especially since it's for a home
built computer and it would be kinda silly to have more computing power
in the filter than in the CPU :-).
| Quote: | Or you could just buy a single chip that does everything you need!
|
If what you say is true, this "chip" could be dangerous!
Bjarni |
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Gareth Magennis
Guest
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| Posted:
Sun Nov 28, 2004 11:23 am Post subject:
Re: Analog filter |
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|
| Quote: | Er, the 8051 has no analog outputs does it? Anyway, the digital side isn't
really a problem. I'm a computing science student and all that, it's just
the conversion of 16 bits of TTL into a voltage that I don't know how to
do.
|
Yes you're right about that, but there are plenty of other microcontrollers
that do. Thre isn't much to converting 16 bits to analogue using an ADC
though. It can be as simple as writing "LDADC xx". The ADC does everything
for you.
Good luck.
Gareth. |
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Gareth Magennis
Guest
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| Posted:
Sun Nov 28, 2004 11:25 am Post subject:
Re: Analog filter |
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| Sorry, that's DAC of course. |
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