Frequency splitting
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I'd like to design a circuit which acted something like an EQ with a
"trigger point."
Essentially, I'd like to take an audio source (say a stereo input) and
have a series of triggers in each frequency band, which if the excitation
in that frequency rose above some point, it would send a stamp line high,
otherwise it would be low.
A friend of mine suggested using a ADC for the entire wave and doing FFT ;
this seems a little CPU-intensive for the stamp. Something like a series
of filter or something seems more like what I'm looking for, though I'm
not really sure thow to construct it. Perhaps filtering out a band with a
band-pass filter and then doing ADC on separate channels?
I'd appreciate any hints.
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
"trigger point."
Essentially, I'd like to take an audio source (say a stereo input) and
have a series of triggers in each frequency band, which if the excitation
in that frequency rose above some point, it would send a stamp line high,
otherwise it would be low.
A friend of mine suggested using a ADC for the entire wave and doing FFT ;
this seems a little CPU-intensive for the stamp. Something like a series
of filter or something seems more like what I'm looking for, though I'm
not really sure thow to construct it. Perhaps filtering out a band with a
band-pass filter and then doing ADC on separate channels?
I'd appreciate any hints.
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
Comments
I've written 560001 code, so I know a *little* about DSP stuff. I was
wondering about the possibilities of pre-filtering (with an actual filter
IC or analog filter) before sending the ADC output to the stamp, which
could just look at a TTL input stream or a high/low pin state. This seems
feasible to me, but I'm not quite sure how to go about it.
On Mon, 16 Oct 2000, Dennis P. O'Leary wrote:
> What you're describing is called a comb filter, in DSP jargon. But it's
> pretty computationally intensive for a stamp, unless Al Williams has already
> designed a PAK that does this [noparse]:)[/noparse].
> Dennis
>
>
Original Message
> From: Sean T. Lamont .lost. [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=dIR5envyfYbRttKgMXQV8UYUWxZgce9huSvYqolz_WJG66Ot0ZThtwIl8Mdb_gbnXW8Ht9OquPfmFrjL5w]lamont@a...[/url
> Sent: Monday, October 16, 2000 6:06 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] Frequency splitting
>
>
>
> I'd like to design a circuit which acted something like an EQ with a
> "trigger point."
>
> Essentially, I'd like to take an audio source (say a stereo input) and
> have a series of triggers in each frequency band, which if the excitation
> in that frequency rose above some point, it would send a stamp line high,
> otherwise it would be low.
>
> A friend of mine suggested using a ADC for the entire wave and doing FFT ;
> this seems a little CPU-intensive for the stamp. Something like a series
> of filter or something seems more like what I'm looking for, though I'm
> not really sure thow to construct it. Perhaps filtering out a band with a
> band-pass filter and then doing ADC on separate channels?
>
> I'd appreciate any hints.
>
>
> Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
> Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
> email: lamont@a... WWW: http://www.serv.net
> "...There's no moral, it's just a lot of stuff that happens". - H. Simpson
>
>
>
>
>
>
>
>
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
pretty computationally intensive for a stamp, unless Al Williams has already
designed a PAK that does this [noparse]:)[/noparse].
Dennis
Original Message
From: Sean T. Lamont .lost. [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=_cMrctlh4mKX8tUOIxJQRO5cxEqgc_HLdMjfG9NgGo5Sw-2Vxd_V6o63a7P5SAQk9dBUT_a9ftoS1ZURq-Mc7O8l]lamont@a...[/url
Sent: Monday, October 16, 2000 6:06 PM
To: basicstamps@egroups.com
Subject: [noparse][[/noparse]basicstamps] Frequency splitting
I'd like to design a circuit which acted something like an EQ with a
"trigger point."
Essentially, I'd like to take an audio source (say a stereo input) and
have a series of triggers in each frequency band, which if the excitation
in that frequency rose above some point, it would send a stamp line high,
otherwise it would be low.
A friend of mine suggested using a ADC for the entire wave and doing FFT ;
this seems a little CPU-intensive for the stamp. Something like a series
of filter or something seems more like what I'm looking for, though I'm
not really sure thow to construct it. Perhaps filtering out a band with a
band-pass filter and then doing ADC on separate channels?
I'd appreciate any hints.
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
pre-filter with a bank of Burr-Brown UAF42 chips, configured as pass-band
filters. They are configured by choosing values for 4 resistors to set the
high and low cut-off frequencies for the pass bands. Configuration equations
are a bit hairy, but the Burr-Brown ap notes give good example descriptions.
These are active filters, which don't require crytal clocks. They are only
2-pole filters, which are probably robust enough for your application. They
cost about $16/chip at DigiKey. If you need steeper filter roll-offs, try
the Maxim 8th order filter chips, which do require crystal clocks.
--Dennis
Original Message
From: Sean T. Lamont .lost. [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=pJbxHRxR29lYJJiy9C5EEx0a6INqZisT9g-YaRydDfI6UXOhwlBQsy1nGEEDU92D1_Ahl2A3p0JtcGv15TU]lamont@a...[/url
Sent: Monday, October 16, 2000 9:24 PM
To: basicstamps@egroups.com.
Subject: RE: [noparse][[/noparse]basicstamps] Frequency splitting
I was sort of indicating that the filtration should be non-DSP based.
I've written 560001 code, so I know a *little* about DSP stuff. I was
wondering about the possibilities of pre-filtering (with an actual filter
IC or analog filter) before sending the ADC output to the stamp, which
could just look at a TTL input stream or a high/low pin state. This seems
feasible to me, but I'm not quite sure how to go about it.
On Mon, 16 Oct 2000, Dennis P. O'Leary wrote:
> What you're describing is called a comb filter, in DSP jargon. But it's
> pretty computationally intensive for a stamp, unless Al Williams has
already
> designed a PAK that does this [noparse]:)[/noparse].
> Dennis
>
>
Original Message
> From: Sean T. Lamont .lost. [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=pJbxHRxR29lYJJiy9C5EEx0a6INqZisT9g-YaRydDfI6UXOhwlBQsy1nGEEDU92D1_Ahl2A3p0JtcGv15TU]lamont@a...[/url
> Sent: Monday, October 16, 2000 6:06 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] Frequency splitting
>
>
>
> I'd like to design a circuit which acted something like an EQ with a
> "trigger point."
>
> Essentially, I'd like to take an audio source (say a stereo input) and
> have a series of triggers in each frequency band, which if the excitation
> in that frequency rose above some point, it would send a stamp line high,
> otherwise it would be low.
>
> A friend of mine suggested using a ADC for the entire wave and doing FFT ;
> this seems a little CPU-intensive for the stamp. Something like a series
> of filter or something seems more like what I'm looking for, though I'm
> not really sure thow to construct it. Perhaps filtering out a band with a
> band-pass filter and then doing ADC on separate channels?
>
> I'd appreciate any hints.
analyzer display".
http://www.njr.com/products/ic/audio.htm
-- Tracy
2%-14% of center freq.)
If it detects a signal in its detection band, the chip pulls pin 8 low. It
requires 3 capacitors and 1 resistor.
Barry
BTW, I'm working on a stand alone FFT chip using the SX28 CPU. I'm
considering providing a TTL output for X user definable frequencies (I don't
know how many can be supported in realtime yet). I'm making it for my own
project, but if it would be useful for anyone else, let me know.
> Message: 12
> Date: Mon, 16 Oct 2000 18:06:02 -0700 (PDT)
> From: "Sean T. Lamont .lost." <lamont@a...>
> Subject: Frequency splitting
>
>
> I'd like to design a circuit which acted something like an EQ with a
> "trigger point."
>
> Essentially, I'd like to take an audio source (say a stereo input) and
> have a series of triggers in each frequency band, which if the excitation
> in that frequency rose above some point, it would send a stamp line high,
> otherwise it would be low.
>
> A friend of mine suggested using a ADC for the entire wave and doing FFT ;
> this seems a little CPU-intensive for the stamp. Something like a series
> of filter or something seems more like what I'm looking for, though I'm
> not really sure thow to construct it. Perhaps filtering out a band with a
> band-pass filter and then doing ADC on separate channels?
>
> I'd appreciate any hints.
>
>
> Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
> Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
> email: lamont@a... WWW: http://www.serv.net
> "...There's no moral, it's just a lot of stuff that happens". - H. Simpson