Simple audio band-pass filters with sharp cut-offs

Discussion in 'Electronic Design' started by mistawizard@gmail.com, Nov 27, 2005.

  1. Guest

    I want to split an audio signal into 5 bands by frequency range (top
    and bottom can be low-pass and high-pass) and send these into speakers
    with moderate power, say 10 watts. I can use amplified speakers if a
    5-way audio amp gets complicated.

    This is not for quality audio, but for educational demo purposes, so I
    don't need an even response and distortion is okay. I'm really looking
    for the sharpest cut-offs I can get, in as simple a box as I can build.
    Can anyone suggest how to accomplish this?

    I haven't made many coils before (rather embarassing for a ham op), but
    I'm fine with simpler circuits. I found a post about an IC that might
    do the trick, but I'm doubting it'll handle audio frequencies.
     
    , Nov 27, 2005
    #1
    1. Advertising

  2. <> wrote in message
    news:...
    >I want to split an audio signal into 5 bands by frequency range (top
    > and bottom can be low-pass and high-pass) and send these into speakers
    > with moderate power, say 10 watts. I can use amplified speakers if a
    > 5-way audio amp gets complicated.
    >
    > This is not for quality audio, but for educational demo purposes, so I
    > don't need an even response and distortion is okay. I'm really looking
    > for the sharpest cut-offs I can get, in as simple a box as I can build.
    > Can anyone suggest how to accomplish this?
    >
    > I haven't made many coils before (rather embarassing for a ham op), but
    > I'm fine with simpler circuits. I found a post about an IC that might
    > do the trick, but I'm doubting it'll handle audio frequencies.


    Don't use coils. Use active filters. I think there is an "Active Filter
    Cookbook" or somesuch floating around out there. You might be able to get a
    copy for a few bucks.
     
    Charles Schuler, Nov 27, 2005
    #2
    1. Advertising

  3. Guest

    On 27 Nov 2005 12:43:38 -0800, wrote:

    >I want to split an audio signal into 5 bands by frequency range (top
    >and bottom can be low-pass and high-pass) and send these into speakers
    >with moderate power, say 10 watts. I can use amplified speakers if a
    >5-way audio amp gets complicated.
    >
    >This is not for quality audio, but for educational demo purposes, so I
    >don't need an even response and distortion is okay. I'm really looking
    >for the sharpest cut-offs I can get, in as simple a box as I can build.
    > Can anyone suggest how to accomplish this?
    >


    No coils are required if you go to
    http://www.linear.com/designtools/filtercad.jsp and get this program.
    Just answer a few questions and you will be presented with a fully
    designed circuit. The IC's are probably going to be surface mount
    ones, but there are easy ways to handle that.

    Jim
     
    , Nov 27, 2005
    #3
  4. <> wrote in message
    news:...
    >I want to split an audio signal into 5 bands by frequency range (top
    > and bottom can be low-pass and high-pass) and send these into speakers
    > with moderate power, say 10 watts. I can use amplified speakers if a
    > 5-way audio amp gets complicated.
    >
    > This is not for quality audio, but for educational demo purposes, so I
    > don't need an even response and distortion is okay. I'm really looking
    > for the sharpest cut-offs I can get, in as simple a box as I can build.
    > Can anyone suggest how to accomplish this?
    >
    > I haven't made many coils before (rather embarassing for a ham op), but
    > I'm fine with simpler circuits. I found a post about an IC that might
    > do the trick, but I'm doubting it'll handle audio frequencies.

    There are several IC's on the market that do exactly this. You could also
    look at active filter circuits based on op-amps. A lot will depend on the
    nature of the signal, and what you want to actually 'do' with the signal.
    A sharp cutoff, will probably involve a several stage filter, and this
    will be much easier with an op-amp, or an IC. This is why inductors have
    almost vanished for this type of application...

    Best Wishes
     
    Roger Hamlett, Nov 27, 2005
    #4
  5. Ben Bradley Guest

    On 27 Nov 2005 12:43:38 -0800, wrote:

    >I want to split an audio signal into 5 bands by frequency range (top
    >and bottom can be low-pass and high-pass) and send these into speakers
    >with moderate power, say 10 watts. I can use amplified speakers if a
    >5-way audio amp gets complicated.
    >
    >This is not for quality audio, but for educational demo purposes, so I
    >don't need an even response and distortion is okay. I'm really looking
    >for the sharpest cut-offs I can get, in as simple a box as I can build.
    > Can anyone suggest how to accomplish this?


    As in so much of engineering, you have competing demands which
    means you have to decide where the tradeoff is. Sharper cutoffs means
    higher pole filters, which require more components with closer
    tolerances. ISTR Lancaster's Active Filter Cookbook discusses this.

    The 'best' solution technically would be an A/D, DSP, and five
    D/A's, as the DSP can be programmed to do quite sharp filters and the
    result will be much more stable than you could possibly get with
    analog components.

    >
    >I haven't made many coils before (rather embarassing for a ham op), but


    You wouldn't want to do this with coils.

    >I'm fine with simpler circuits. I found a post about an IC that might
    >do the trick, but I'm doubting it'll handle audio frequencies.
     
    Ben Bradley, Nov 27, 2005
    #5
  6. "Charles Schuler" <> wrote in message
    news:...
    > [...]
    > Don't use coils. Use active filters. I think there is an "Active Filter
    > Cookbook" or somesuch floating around out there. You might be able to get
    > a copy for a few bucks.


    You'll be well served by Don Lancaster's "Active Filter Cookbook", 2ed.,
    ISBN 075062986X.

    Or, google "Sallen-Key bandpass filter" and you'll probably come up with
    something.
     
    Walter Harley, Nov 28, 2005
    #6
  7. "Walter Harley" () writes:
    > "Charles Schuler" <> wrote in message
    > news:...
    >> [...]
    >> Don't use coils. Use active filters. I think there is an "Active Filter
    >> Cookbook" or somesuch floating around out there. You might be able to get
    >> a copy for a few bucks.

    >
    > You'll be well served by Don Lancaster's "Active Filter Cookbook", 2ed.,
    > ISBN 075062986X.
    >

    Is that still being printed by a traditional publisher, or does
    the poster have to visit Don's site, http://www.tinaja.com to get it?

    Michael

    > Or, google "Sallen-Key bandpass filter" and you'll probably come up with
    > something.
    >
    >
    >
     
    Michael Black, Nov 28, 2005
    #7
  8. Guest

    Beautiful! I'll check out the Active Filter Cookbook (my library has
    it!), but if there's a good IC for it, so much the better. I just want
    to take a line-level or microphone input (not powered) and have it put
    the sound out at line level (I'll feed them into amplified "computer"
    speakers), each representing a different frequency range (probably
    0-200Hz, 200-400, 400-800, 800-1600, 1600+) so I can turn channels on
    and off, and kids can experience fourier decomposition concepts and
    filtering in real-time. Again, quality is not a big issue (although
    reliability is).

    Can you suggest where to look nowadays for ICs like this, or an IC that
    would work well? I used to use the old radio shack semiconductor
    reference. It's been a while. I'm guessing the Active Filter Cookbook
    doesn't include ICs like this, so are there any "cookbook" schematics
    for these handy ICs?

    Thanks for all the great advice!

    > There are several IC's on the market that do exactly this. You could also
    > look at active filter circuits based on op-amps. A lot will depend on the
    > nature of the signal, and what you want to actually 'do' with the signal.
    > A sharp cutoff, will probably involve a several stage filter, and this
    > will be much easier with an op-amp, or an IC. This is why inductors have
    > almost vanished for this type of application...
    >
    > Best Wishes
     
    , Nov 28, 2005
    #8
  9. wrote:
    > Beautiful! I'll check out the Active Filter Cookbook (my library has
    > it!), but if there's a good IC for it, so much the better. I just want
    > to take a line-level or microphone input (not powered) and have it put
    > the sound out at line level (I'll feed them into amplified "computer"
    > speakers), each representing a different frequency range (probably
    > 0-200Hz, 200-400, 400-800, 800-1600, 1600+) so I can turn channels on
    > and off, and kids can experience fourier decomposition concepts and
    > filtering in real-time. Again, quality is not a big issue (although
    > reliability is).
    >
    > Can you suggest where to look nowadays for ICs like this, or an IC that
    > would work well? I used to use the old radio shack semiconductor
    > reference. It's been a while. I'm guessing the Active Filter Cookbook
    > doesn't include ICs like this, so are there any "cookbook" schematics
    > for these handy ICs?


    In the cook book, look for a 4 pole bandpass filter. This produces a
    double peak result (one near the low frequency end of the band and one
    at the high frequency end of the band) with sharp enough roll off at
    the edges for this application.

    Of you can combine a 2 pole high pass (to cut the low end) and a 2
    pole low pass (to cut the high end). If you choose a bi quad or state
    variable design for these, you will be able to adjust the cut off
    frequencies with a pot without altering much of anything else about
    the response. Good for demonstrating what more bits in the Fourier
    does for the result.

    Or you can use just 2 pole bandpass filters (single peak response)
    made as a bi quad or state variable and adjust both the center
    frequency and bandwidth as desired. These take 3 opamps each, but
    since you can get 4 opamps in a single package for less than a dollar,
    this is not much of a problem. The LM324 is a good choice for cheap
    quad opamp that runs on a wide range of supply voltages with low
    supply current, if sound quality is not a big concern (it does produce
    a bit of distortion at higher audio frequencies). Common as dirt.
    http://www.onsemi.com/pub/Collateral/LM324-D.PDF
     
    John Popelish, Nov 28, 2005
    #9
  10. Ben Bradley Guest

    On 28 Nov 2005 00:29:19 -0800, ""
    <> wrote:

    >Beautiful! I'll check out the Active Filter Cookbook (my library has
    >it!), but if there's a good IC for it, so much the better. I just want
    >to take a line-level or microphone input (not powered) and have it put
    >the sound out at line level (I'll feed them into amplified "computer"
    >speakers), each representing a different frequency range (probably
    >0-200Hz, 200-400, 400-800, 800-1600, 1600+) so I can turn channels on
    >and off, and kids can experience fourier decomposition concepts and
    >filtering in real-time. Again, quality is not a big issue (although
    >reliability is).


    Aha. In this application you don't neccesarily need the steep
    cutoff slopes. You can use a fairly low-Q (perhaps in the 0.3 to 1
    range) bandpass filters, one for each band.
    Another idea comes to mind: a five-band audio graphic equalizer, as
    made by just about everyone in the '70's and '80's. Used ones are
    surely plentiful and cheap nowadays. Even 7-band and 10-band EQ's are
    common and cheap. Look on ebay. In such an EQ, all the filters are
    summed to one output, but you can remove the summing network and run
    each filter output to a separate amplifier/speaker. This is easier
    than making your own circuit.

    >Can you suggest where to look nowadays for ICs like this, or an IC that
    >would work well? I used to use the old radio shack semiconductor
    >reference. It's been a while. I'm guessing the Active Filter Cookbook
    >doesn't include ICs like this, so are there any "cookbook" schematics
    >for these handy ICs?


    >Thanks for all the great advice!
    >
    >> There are several IC's on the market that do exactly this. You could also
    >> look at active filter circuits based on op-amps. A lot will depend on the
    >> nature of the signal, and what you want to actually 'do' with the signal.
    >> A sharp cutoff, will probably involve a several stage filter, and this
    >> will be much easier with an op-amp, or an IC. This is why inductors have
    >> almost vanished for this type of application...
    >>
    >> Best Wishes
     
    Ben Bradley, Nov 28, 2005
    #10
  11. "Michael Black" <> wrote in message
    news:dme162$r4u$...
    >>
    >> You'll be well served by Don Lancaster's "Active Filter Cookbook", 2ed.,
    >> ISBN 075062986X.
    >>

    > Is that still being printed by a traditional publisher, or does
    > the poster have to visit Don's site, http://www.tinaja.com to get it?


    I bought mine from Powell's a couple years ago, and it was still in print
    then. It's on the Newnes imprint.
     
    Walter Harley, Nov 28, 2005
    #11
  12. Joel Kolstad Guest

    "Walter Harley" <> wrote in message
    news:...
    >>> You'll be well served by Don Lancaster's "Active Filter Cookbook", 2ed.,
    >>> ISBN 075062986X.


    Good recommendation for audio range active filters.

    >> Is that still being printed by a traditional publisher, or does
    >> the poster have to visit Don's site, http://www.tinaja.com to get it?

    >
    > I bought mine from Powell's a couple years ago, and it was still in print
    > then. It's on the Newnes imprint.


    I got mine a year or so ago from Marlin P. Jones who, at the time, was selling
    off a bunch that were autographed by Don himself for no more than the regular
    price of the book.
     
    Joel Kolstad, Nov 29, 2005
    #12
  13. Joel Kolstad Guest

    "John Popelish" <> wrote in message
    news:...
    > wrote:
    >> Beautiful! I'll check out the Active Filter Cookbook (my library has
    >> it!), but if there's a good IC for it, so much the better.


    One other suggestion: At audio frequencies, switched capacitor filters are
    quite good, and since you don't care about a little distortion anyway, you can
    use a dirt simple anti-image filter at the output.

    The beauty of switched capacitor filters is that 'everything' scales with the
    input clock frequency. I.e., if you design the thing so that you end up with
    a 5kHz Q=10 bandpass with an input clock of, say, 1MHz, if you halve the input
    clock to 500kHz you'll have a 2.5kHz Q=10 bandpass filter. Another nice
    benefit is that most of the tuning elemenets for active filter ICs are on-chip
    and thereby tend to be matched (ratioed) to one another much better than you'd
    be able to achieve by just randomly choosing components (of the same nominal
    value) from your parts drawer; if you decide to start building significantly
    narrower filters that what you've specified, this can become significant. (I
    had a professor who claimed that 'all good IC designs are beautiful to look
    at,' and while I think that's sometimes just wishful thinking and have even
    read papers suggesting as much, his point was that you can derive a few simple
    rules for IC layout that attempt to minimize component ratio tolerances and
    these rules end up making symmetrical patterns that tend to be aesthetically
    pleasing as well...)

    The Linear Tech LTC1562 might be a good place to start...
     
    Joel Kolstad, Nov 29, 2005
    #13
  14. ehsjr Guest

    Joel Kolstad wrote:

    >
    >
    > I got mine a year or so ago from Marlin P. Jones who, at the time, was selling
    > off a bunch that were autographed by Don himself for no more than the regular
    > price of the book.
    >
    >
    >


    Good information! I looked - MPJA still sells them.
    http://www.mpja.com/directview.asp?product=7245 BK

    Thanks,
    Ed
     
    ehsjr, Nov 29, 2005
    #14
  15. Ben Bradley Guest

    On Mon, 28 Nov 2005 09:26:20 -0800, "Walter Harley"
    <> wrote:

    >"Michael Black" <> wrote in message
    >news:dme162$r4u$...
    >>>
    >>> You'll be well served by Don Lancaster's "Active Filter Cookbook", 2ed.,
    >>> ISBN 075062986X.
    >>>

    >> Is that still being printed by a traditional publisher, or does
    >> the poster have to visit Don's site, http://www.tinaja.com to get it?

    >
    >I bought mine from Powell's a couple years ago, and it was still in print
    >then. It's on the Newnes imprint.
    >


    http://www.bookfinder.com has many copies, a few are quite cheap, but
    most prices are in the $20-$30 range, where the new copy prices start.

    I found this amusing entry under the title "Active-Filter Cookbook by
    Lancaster, Donald E.":

    "TRUE COLLECTABLE, AUTHOR'S SIGNATURE Tight, straight, clean, cover
    shows wear as well as edges of text. This book has been used but not
    in your normal cooking. $19.50"
     
    Ben Bradley, Nov 30, 2005
    #15
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Replies:
    4
    Views:
    395
    john jardine
    Nov 29, 2005
  2. Fred Bartoli

    DBM and constant R band pass filters.

    Fred Bartoli, Apr 18, 2004, in forum: Electronic Design
    Replies:
    3
    Views:
    353
    Joerg
    Apr 18, 2004
  3. Replies:
    10
    Views:
    2,652
  4. Tony R. Kuphaldt

    Band-Pass Filters

    Tony R. Kuphaldt, Jun 24, 2010, in forum: Filters
    Replies:
    0
    Views:
    1,406
    Tony R. Kuphaldt
    Jun 24, 2010
  5. stepylo
    Replies:
    1
    Views:
    637
    Militoy
    Oct 5, 2010
Loading...

Share This Page