Re: Best way to measure precise harmonics?

On Oct 22, 9:26 pm, Tom Bruhns <k7...@xxxxxxx> wrote:
On Oct 22, 8:42 pm, JosephKK <joseph_barr...@xxxxxxxxxxxxx> wrote:



Ken S. Tucker dynam...@xxxxxxxxxxxx posted to sci.electronics.design:

Thanks Joseph & Mr. Walpert as well.

On Oct 21, 5:28 pm, JosephKK <joseph_barr...@xxxxxxxxxxxxx> wrote:
Ken S. Tucker dynam...@xxxxxxxxxxxx posted to
sci.electronics.design:

Thanks for your "feeback" (pun intended) Tom.

On Oct 20, 1:30 pm, Tom Bruhns <k7...@xxxxxxx> wrote:
...
Ken said
Interesting, I'll pull this quote,
" hard specs on the distortion introduced
by the acoustic to electrical transducer:"

Just so you guys know I'm serious about this
subject, I/we designed this unit,

http://www.trak4.com/earco/index.html

and I respect the problem of acoustic transducers.
At that site are recorded wave forms of Loons,
(let me know if you have any problems getting
their call, my current system hasn't got audio).

I'd get the Loons to yell by recording them and
then replaying their call over the lake. They'd
show at my dock yelling back. So I relied on
my "tin ear" (and others) to inform me of distortion.
I wasn't crazy about the science of the test but
what choice did I have?
Regards
Ken S. Tucker

No problem getting the loon sounds to play, though there's a
tremendous amount of echo in them, it seems like!

Thanks for listening.
The Loons were a few hundred yards from shore
and recorded at night, so the shoreline trees
would bounce the sound quite a bit, those guys
are loud! That haunting echo might be part of the
uniqueness of the recording.

I hadn't directly addressed your original posting where you
asked how
good modern ADCs are, and about analyzing the digitized sounds.
The best off-the-shelf audio converters I know about are 24 bit,
can digitize with output rate of 96k and 192k samples/second in
addition to the old 48k, and have distortion products typically
at the part per
million level. The noise is pretty darned good too. I suspect
it's unlikely that you'll find a transducer that linear, at
least not with loud sounds, and it's not trivial by any means to
make a preamp with such low distortion (though some of the
modern op amps have helped a lot with that).

My audio frequency ADC experience was with
audio scramblers for security, like spy stuff.
The audio was digitized via an ADC-ROM and
anti-ROM'd at the recieving end.

One way to view an FFT is that it compares the input signal with
sines and cosines at the frequencies corresponding to the FFT
points (also
commonly called "bins"). An advantage of the DFT is that you
can do that comparison for any spot frequency, and you're not
limited to the linear frequency spacing of the FFT; but of
course, it's much slower
if you want to do a LOT of points. On the other hand, there's a
DFT algorithm that lets you calculate as the data comes in, and
as soon as you've finished collecting the data, just a very few
operations gives you the final answer from the DFT -- you can
run several of those in parallel if you want.

And of course, you can design a filter or detector that is
"optimal" in some sense, using things you know about the
waveform you're
analyzing. An FFT is a good general-purpose spectral analysis
tool, but it likely won't be the _best_ tool for some specific
application. Cheers,
Tom

I worked with servicing and developing Medical
Ultrasound equipment, where the audio frequency
runs to 10Mhz, that's fun stuff. Stuff is ingenious,
all dedicated to get a good image.
Regards
Ken

I personally found the recordings unacceptable. The noise was far
larger than the loon calls were. Make a point of checking an audio
file before placing it on your web site please.

Thanks for pointing that out.
The noise is mainly from a nearby waterfall, which
generates white noise, we should put that on the
site.
I've tried to eliminate "waterfall" noise using a
graphics equalizer but with mixed results.
I designed a filter in the EAR that softly favors
about 4kHz, it's a trade-off.

We recorded the sounds on to cassette, then
fed them into the wavefile back in the 90's.

Incidentally, we've only had one field failure.
A Woodpecker started pecking the hole and
that's were the microphone is, behind a light
screen, and it damaged the mike.
The customer (a wealthy bird watcher) makes
an appointment and comes to the office.
I swapped in a new PCB at cost ($50), and
put heavy screening over the hole.
He bought another one because he wanted
stereo, putting one at each end of his river
front property.
I expected lightning striking the units but that
hasn't been reported.

We did echo testing of the mounting and
minimized that effect with foam.
All customers are satisfied, but we're working
on improvements!
Regards
Ken S. Tucker

What i heard was more like excess gain going into oscillation.
Squeals and hums and such. It was kind of weird, when the loon calls
broke through they were clear.

Well, the file is 8 bit uncompressed at 11025 samples/second. Don't
expect a whole lot out of that, of course. I'm looking, right now, at
a section from near the start of the recording, about 8 seconds from
the start. I can see some energy at 60Hz and its harmonics, up to
about 360Hz,

Yeah! We worked hard to eliminate 60Hz...etc,
fancy filtering, shielded cable is standard too,
it's another trade-off, costs go up to take the 60hz
down a bit more for increasingly expensive filters.
Mainly it's a subjective call, boosting the amp
volume to where 60hz is audiable would also make
a cricket sound like a "rock concert".

but by far the most energy is in the 0.8kHz to 1.8kHz
range. A typical segment is a warble between 1.0 and 1.2kHz, about 10
cycles of warble per second, with a very slightly falling average
frequency. That lasts about half a second, and is followed a very
short gap later by either about the same thing, or something similar
but at generally not quite as distinct from about 1.2 to 1.4kHz, same
sort of warble.

Hmmm, might make a good cell phone "ringtone".

Perhaps the most remarkable thing to me is that the recording goes on
for several seconds at a time with only two or three dB variation in
amplitude. Seems like that would get monotonous very quickly. ;-)

Yup, after awhile you just tune them out,
them Loons will spend all night humping,
sort of a lullaby.

Cheers,
Tom

Thanks Tom.
Ken

.

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  • Re: Best way to measure precise harmonics?
    ... my "tin ear" to inform me of distortion. ... uniqueness of the recording. ... The best off-the-shelf audio converters I know about are 24 bit, ... The noise is pretty darned good too. ...
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  • Re: Best way to measure precise harmonics?
    ... my "tin ear" to inform me of distortion. ... uniqueness of the recording. ... The best off-the-shelf audio converters I know about are 24 bit, ... The noise is pretty darned good too. ...
    (sci.electronics.design)
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    (sci.electronics.design)
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