"Henry Kolesnik" wrote in
message
. net
There's a good example of a 3D plot he
http://www.spectraplus.com/screenshots.html#3d
Has anyone used this software?

Yes, but not for exactly that purpose.

Here's a sample of my usage of Spectra:

http://www.pcavtech.com/soundcards/lynxtwo/

On Mon, 19 Feb 2007 15:16:29 -0600, "Henry Kolesnik"
wrote:

There's a good example of a 3D plot he
http://www.spectraplus.com/screenshots.html#3d
Has anyone used this software?

Hi Hank,

Yes, I have. It is exceedingly expensive, but you can probably get 30
days of free use if you have a one-time knock off project. Of course,
it may take 30 days to figure it out.

FFT analyzers are a dime a dozen, but few know how to use them
accurately - or are even aware of what can be done with them. Bob's
complaint, notwithstanding, a 1024 bin FFT employing the proper mixing
inputs can resolve any note on a guitar to within hundredths of a
cycle. I am sure this is of no interest to you, however.

What are you trying to measure? The dime a dozen analyzers (meaning
free, or packaged with other software) can do enough if you are not
particularly demanding.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message

On Mon, 19 Feb 2007 15:16:29 -0600, "Henry Kolesnik"
wrote:

There's a good example of a 3D plot he
http://www.spectraplus.com/screenshots.html#3d
Has anyone used this software?

Hi Hank,

Yes, I have. It is exceedingly expensive, but you can
probably get 30 days of free use if you have a one-time
knock off project. Of course, it may take 30 days to
figure it out.

FFT analyzers are a dime a dozen, but few know how to use
them accurately - or are even aware of what can be done
with them. Bob's complaint, notwithstanding, a 1024 bin
FFT employing the proper mixing inputs can resolve any
note on a guitar to within hundredths of a cycle. I am
sure this is of no interest to you, however.

Over the years, the most useful FFT software I've had, is the (fairly
simple) FFT analyzer in Audition/CEP. It's big plus is the ability to use
the Audition/CEP audio editor to select portions of real-world waveforms,
and to use the wave generation and modification features to create waves for
use in analysis and testing.

Amy, Bob, Richard
Thanks for your response and interest. I'm retired used to be an
engineer
before management laid waste to that. I've started taking weekly guitar
lessons over a year ago and slowly getting a bit better. It's a hell
of a challenge at 66. I want
to buy a better guitar and all guitars don't sound the same, even the
same model. One shouldn't expect them to because they're all made from
different cuts of wood and assembled by human hands. What amazed me is
that the materials used for the nut, neck, saddle and bridge as well as
the mfg and age of the strings have a noticeable effect on the sound.
The bridge pins, angle of the strings out of the bridge pin holes and
tuners also have effects.
In the last year I found at least four guitars that I really liked, 3
used ones and a new one all over a $1000.00 but I passed because I'm not
that impulsive or flush with cash. A good player can make just about
any guitar sound good, or a hell of a lot better than me.
I'm into ham radio also and last year at hamfest I traded for an HP
3582A spectrum analyzer but the learning curve is a bit steep for me.
So unless I can find an experienced user or devote much more time to it
I'm going to have to trade it.
Last week I won an HP 3561A on ePay but it has a problem that I hope I
can fix. In the meantime I thought it might make sense to scope out
sound cards and related software. I know a lot of hams use sound cards
for various & different applications and it's about time I took a wack
at one and what better way than trying to figure out what it is that
makes one guitar sound so much better than another. Or if changing the
nut, saddle or bridge pins really improves the sound or is it just
wishful thinking.
And I can make use of it for ham radio weak signal detection and
analysis.
I used a term; slab diagrams which may be known as stack diagrams. I'm
interested in watching a plucked and later chords as they decay over
time in sort of a 3D plot. There's a good example of what I'm looking
for in the HP catalog describing the HP 3561A.
tnx

73
Hank WD5JFR

"Richard Clark" wrote in message
...
On Mon, 19 Feb 2007 15:16:29 -0600, "Henry Kolesnik"
wrote:

There's a good example of a 3D plot he
http://www.spectraplus.com/screenshots.html#3d
Has anyone used this software?

Hi Hank,

Yes, I have. It is exceedingly expensive, but you can probably get 30
days of free use if you have a one-time knock off project. Of course,
it may take 30 days to figure it out.

FFT analyzers are a dime a dozen, but few know how to use them
accurately - or are even aware of what can be done with them. Bob's
complaint, notwithstanding, a 1024 bin FFT employing the proper mixing
inputs can resolve any note on a guitar to within hundredths of a
cycle. I am sure this is of no interest to you, however.

What are you trying to measure? The dime a dozen analyzers (meaning
free, or packaged with other software) can do enough if you are not
particularly demanding.

73's
Richard Clark, KB7QHC

On Mon, 19 Feb 2007 14:08:54 -0800, Richard Clark
wrote:

On Mon, 19 Feb 2007 15:16:29 -0600, "Henry Kolesnik"
wrote:

There's a good example of a 3D plot he
http://www.spectraplus.com/screenshots.html#3d
Has anyone used this software?

Hi Hank,

Yes, I have. It is exceedingly expensive, but you can probably get 30
days of free use if you have a one-time knock off project. Of course,
it may take 30 days to figure it out.

FFT analyzers are a dime a dozen, but few know how to use them
accurately - or are even aware of what can be done with them. Bob's
complaint, notwithstanding, a 1024 bin FFT employing the proper mixing
inputs can resolve any note on a guitar to within hundredths of a
cycle. I am sure this is of no interest to you, however.

Yes, you can easily resolve to 100ths of a cycle, but not from
a native FFT. (See my other response.) You can do it from
the waveform by measuring the time between cycles. That's
one of the methods I'm working on. The other is to do it from
the FFT via peak interpolation. The waveform method will
be very accurate with simple static waveforms, but I expect it
will have trouble with the 2nd harmonic of a plucked string,
which is not an integer multiple so "rolls" through the waveform.
The FFT interpolator will not have the same raw accuracy, and must
have absolutely separated spectral peaks since it assumes the
one it's interpolating is the only one. I'm not hopeful it can be
made good enough to tune a guitar, at least not in the bottom
octave where the harmonics land on adjacent spectral lines.

Best regards,


Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!

On Mon, 19 Feb 2007 10:34:50 -0800, Richard Clark
wrote:

On Mon, 19 Feb 2007 14:06:30 GMT, (Bob Masta)
wrote:

FFT size is 1024 points, so you won't be able to use
this for tuning your guitar, if that's what you had in mind.

Hi Bob,

Why not? 1024 points (bins) has enough resolution to shake out every
note on a Hawaiian slide guitar. The only care is selecting the
sampling rate and most FFT packages should be able to resolve
exceedingly fine.


The problem is that the line resolution of an FFT is the sample
rate divided by the number of time points. So with 44100 Hz
sample rate and 1024 points you get a bit over 43 Hz per line.
So the first non-DC spectral line would be 43 Hz, which is about
a low F on a bass guitar, and the very next line would be the F
an octave above that... you'd miss an entire octave!

The standard musical note frequencies (semitones) differ
from each other by about 6% (12th root of 2, since there are
12 notes in an "octave"). But you need much better
resolution than this for tuning, typically a "cent" or so,
namely 1/100 of a semitone or .06%. At 43 Hz that
works out to about 0.026 Hz. A 64K-point FFT
at 44100 Hz will have a native resolution of 0.67 Hz,
which still isn't good enough... but at 64K samples,
you are looking at 1.48 seconds of sound. If the
pitch changes over that interval, the spectral peak
will be smeared even further.

If you attempt to beat this game by going to lower
sample rates, note that frequency resolution is
still proportional to the inverse of the total sampling
interval. So if you tried to use the 1K FFT but sample at
44100 / 64 = 689 Hz to get the same (inadequate)
resolution as the above 64K FFT, you'd still need 1.48
seconds of sound. Sound cards don't sample that
low intrinsically (typically 8K lower limit, 4K on old
Sound Blasters), but you might manage using sample
rate conversion (either Windows or sound card built-in).
I haven't tried this, but I suspect that it would not be a satisfying
experience due to the s-l-o-w time response.

Best regards,





Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!

On Tue, 20 Feb 2007 14:04:19 GMT, (Bob Masta)
wrote:

On Mon, 19 Feb 2007 10:34:50 -0800, Richard Clark
wrote:

On Mon, 19 Feb 2007 14:06:30 GMT, (Bob Masta)
wrote:

FFT size is 1024 points, so you won't be able to use
this for tuning your guitar, if that's what you had in mind.

Hi Bob,

Why not? 1024 points (bins) has enough resolution to shake out every
note on a Hawaiian slide guitar. The only care is selecting the
sampling rate and most FFT packages should be able to resolve
exceedingly fine.


The problem is that the line resolution of an FFT is the sample
rate divided by the number of time points. So with 44100 Hz
sample rate and 1024 points you get a bit over 43 Hz per line.
So the first non-DC spectral line would be 43 Hz, which is about
a low F on a bass guitar, and the very next line would be the F
an octave above that... you'd miss an entire octave!

Hi Bob,

What you describe here, and that which followed, is a problem of
either hardware (I design my own) or a perception of Fourier
techniques that is constrained to common applications.

The trick is one that is encountered quite commonly with RF designers
(and those Hams that actually practice the craft instead of being
appliance operators) - it is called mixing. Or to describe it with
more precision (as an audio crowd has a restricted meaning for the
term "mixing") heterodyning or modulating/demodulating. Simply put,
the data channel is pre-processed by multiplying it with a reference
cosine before being passed onto the FFT. (Although this sounds like
windowing, it is not.) Of course, the output of the FFT has to have
its units recast. In the old days, this was called "zooming" or an
arbitrary view of a single frequency encompassed by a span of far
higher resolution than that obtained from a simple transform. I would
quickly point out that the simple transform is still performed (same
bin interval, same bin count), but it has been augmented.

This technique, plus a waterfall display, is useful in tracing down
mechanical problems in journals, bearing races (with bearing run-out
or ball defect) and bad gear meshes. It also relates to Hank's desire
to test individual construction components in the guitar as all of
these problems relate to a subtle data inflection that can be
destructive in machinery, or discordant in music. The zoom feature
can reveal these defects with remarkable resolution. As I said, the
FFT as originally described can differentiate every note of an
Hawaiian slide guitar. Perhaps I should have added the proviso:
provided you use a synchronized tracking generator for mixing.
However, given this can be done digitally (no one needs a hardware
oscillator), no change in hardware is necessary. All the data that is
needed is already there.

www.daqarta.com
by the way, this seems to be a dead link. (later) I take that back,
but it took a lot of retries over the span of an hour.

Further, it seems you have a lot of what I mention above covered in
your pages, by parts, but none of them encompass the whole of
"zooming."

And for your page on windowing, drop me an email if you would like to
see some pascal routines embodying some very tight windows. These
came from my time with HP whose chief engineer soon after departed for
a chair at some eastern university.

73's
Richard Clark, KB7QHC

On Wed, 21 Feb 2007 23:47:39 -0800, Richard Clark
wrote:

On Tue, 20 Feb 2007 14:04:19 GMT, (Bob Masta)
wrote:

On Mon, 19 Feb 2007 10:34:50 -0800, Richard Clark
wrote:

On Mon, 19 Feb 2007 14:06:30 GMT, (Bob Masta)
wrote:

FFT size is 1024 points, so you won't be able to use
this for tuning your guitar, if that's what you had in mind.

Hi Bob,

Why not? 1024 points (bins) has enough resolution to shake out every
note on a Hawaiian slide guitar. The only care is selecting the
sampling rate and most FFT packages should be able to resolve
exceedingly fine.


The problem is that the line resolution of an FFT is the sample
rate divided by the number of time points. So with 44100 Hz
sample rate and 1024 points you get a bit over 43 Hz per line.
So the first non-DC spectral line would be 43 Hz, which is about
a low F on a bass guitar, and the very next line would be the F
an octave above that... you'd miss an entire octave!

Hi Bob,

What you describe here, and that which followed, is a problem of
either hardware (I design my own) or a perception of Fourier
techniques that is constrained to common applications.

The trick is one that is encountered quite commonly with RF designers
(and those Hams that actually practice the craft instead of being
appliance operators) - it is called mixing. Or to describe it with
more precision (as an audio crowd has a restricted meaning for the
term "mixing") heterodyning or modulating/demodulating. Simply put,
the data channel is pre-processed by multiplying it with a reference
cosine before being passed onto the FFT. (Although this sounds like
windowing, it is not.) Of course, the output of the FFT has to have
its units recast. In the old days, this was called "zooming" or an
arbitrary view of a single frequency encompassed by a span of far
higher resolution than that obtained from a simple transform. I would
quickly point out that the simple transform is still performed (same
bin interval, same bin count), but it has been augmented.

This technique, plus a waterfall display, is useful in tracing down
mechanical problems in journals, bearing races (with bearing run-out
or ball defect) and bad gear meshes. It also relates to Hank's desire
to test individual construction components in the guitar as all of
these problems relate to a subtle data inflection that can be
destructive in machinery, or discordant in music. The zoom feature
can reveal these defects with remarkable resolution. As I said, the
FFT as originally described can differentiate every note of an
Hawaiian slide guitar. Perhaps I should have added the proviso:
provided you use a synchronized tracking generator for mixing.
However, given this can be done digitally (no one needs a hardware
oscillator), no change in hardware is necessary. All the data that is
needed is already there.

www.daqarta.com
by the way, this seems to be a dead link. (later) I take that back,
but it took a lot of retries over the span of an hour.

Further, it seems you have a lot of what I mention above covered in
your pages, by parts, but none of them encompass the whole of
"zooming."

And for your page on windowing, drop me an email if you would like to
see some pascal routines embodying some very tight windows. These
came from my time with HP whose chief engineer soon after departed for
a chair at some eastern university.

73's
Richard Clark, KB7QHC

Richard:

Thanks for your detailed post. I am aware of the "zoom"
approach, but have not implemented it yet. The cosine
multiplication down to baseband is the easy part; the part
that has put me off is the pesky decimating filter.

For others reading this, the basic idea of the zoom FFT is that
if you want to "zoom in on" some frequency region at
higher resolution, you multiply the incoming signal by the
center of the desired range. From that old high school
trig formula for the product of sinusoids, you get a bunch of
sum and difference components. So the center of the
target band ends up at 0 Hz since you multiplied it by a
sinusoid at the center frequency, and all the rest of
the original spectrum is now spreading out on either
side of 0. Now, if you low-pass filter this mess you can
re-sample it at a much lower frequency. The filter has
to be set so there is nothing of significance above half
of the new sample rate, just as for the orignal ADC (or
you get aliasing errors).

Then you take an FFT of the same size (1024 or whatever)
samples, but at the new lower sample rate. If the new rate is
1/100 of the original, the resolution of the spectrum is improved
x100. Another way to think about this is that if you only wanted
to zoom in on the low end of the spectrum, you wouldn't need to
do the cosine multiply, filter, or resampling... you could just reduce
the base sample rate to 1/100 (if your sound card permitted, and had
its anti-alias filters set for that) and get exactly the same results.

Note that this gives exactly the same resolution as an FFT that is
x100 larger, where you only get to see 1/100 of the whole spectrum.
Also note that an x100 increase in resolution takes x100 increase
in sample time, so you must insure that the signal is stable over that
interval or you will get spectral peak smearing... there is no free
lunch here! This is no problem for Richard's examples of bearings
and gear meshes, but I'd expect troubles with most music since
it is so dynamic.

Anyway, back to my original lament: The low-pass filtering and
resampling would be quite inefficient if done by conventional
approaches, but there are apparently some elegant solutions
that do both functions in one block, reusing it over and over
to get successive halvings of the sample rate. My problem is
that I have only seen this described in theoretical terms with
simple block diagrams, leaving the exact coefficients, etc, as
"an excercise for the reader". Searching the Web I find that
others are apparently as left out in the cold by this as I am,
and there is no example code, hints, or tips to be found.

So, until this particular reader either gets struck by a flash
of insight or takes the time to read up on this enough to
get a whole lot smarter, the zoom FFT is on a back burner.

(Richard, I'll Email you about those window routines...
many thanks for the offer!)

Best regards,





Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!