Sub Audio Frequency Doubler

Hi,

Do someone know a simple way to double a low frequency complex wave signal, real time, using an simple analog circuit?

I need to rise the low frequency of a whale sound ( lower than 20hz) to an human audible level, around 40hz.

Bye Jacques

Reply to
Jacques St-Pierre
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I would suggest that the most effective way to make the signal "audible" is to use the signal to frequency-modulate a tone near the mid-range of human hearing. This is not the original "sound" by any stretch.

Simply doubling a 20Hz signal to 40Hz will be complex and of very limited utility as you are still at the extreme of audible hearing. I know people will tell me I'm wrong, but these are the same people who tell me that 20kHz fundamental tones are important to me too, and I simply cannot hear those either :-).

Another possibilty is to record (probably digitally) one-second snippets of your sub-20Hz signal, and then play back that snippet 20 times faster 20 times over every second.

Again, the details of how you make the signal audible will depend on what parts of the sound you think are important.

Tim.

Reply to
Tim Shoppa

Creating false sounds ? Mixing it with itself does that. See MC1496 Why not just :

1) have the loudspeaker transmit the sound, it won't be audible, but with an open speaker it will be visible, or feelable with a finger 2) visualize it on a scope

Rene

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Reply to
Rene Tschaggelar

Digitize each "whole cycle" of the sound, play them out at interger multiples of the original sampling rate. This will give the most accurate representation of the original sound.

I've done this, it works.

Luhan

Reply to
Luhan

Nicolet (I think) made a "Ubiquitous Spectrum Analyzer". It digitized a slow signal, ran it around in a circle, fast, and DAC'd that into a swept bandpass filter. So it would give a continuous, fast spectrum of slow signals. FFTs killed it off, of course.

This has some nasty windowing problems, lots of artifacts, but the technique is probably OK for listening to whale noises. One could digitize the signal and apply a soft sliding window function before doing the twirl-around speedup thing.

A sound card and a PowerBasic program would do it with an afternoon of futzing.

Or you could do the continuous-sample thing, sliding window, FFT several times a second, shift, de-FFT, and play.

John

Reply to
John Larkin

If you just want to hear a transformed version of the 20 Hz signal, you can build an analog circuit that includes n cascaded stages, with each stage doing all this:

- DC removal.

- Amplification.

- Full-wave rectification (with a superdiode (diode using op-amps)).

Cascading n stages, 20 Hz would turn into 20*2^n Hz. The output will sound horrible, but you should be able to hear it, and variations in the input amplitude/frequency should be noticeable at the output, which is what you want (otherwise you just need a presence/absence detector).

Best,

Reply to
Mochuelo

Audio frequency doubling, I use a double diode "full wave" method off of an OP amp output for "higher frequencies > 400 hz". It works great for a musical sound but would distort the true sound reproduction you are trying to capture.

For fun here is a sub-harmonic "Whale call" generated from my own design of a two transistor theremin.

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(.mp3 115k)

Crank up the sub-woofer, 40 hz sounds pleasant, 10 hz needs a slightly distorted wave shape so you can hear speaker popping instead of an undetectable quiet smooth sine wave..

  • * * Christopher

Temecula CA.USA

formatting link

Reply to
Christopher

A simple differential amp made from two transistors can rectify and square the driving signal. I do not know how it will sound though. Maybe twice the same you should have 4 times the original frequency, which should be audible then.

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ciao Ban
Apricale, Italy
Reply to
Ban

I'm wondering why you are asking to double. I have done the opposite making a

1/2 division of frequency for disco type things. Is it polyphonic?

Why not get the sound to an even higher harmonic? I think it would work and sound better.

greg

Reply to
GregS

There was a project in ELEKTOR for a ultrasound convertor device, making it possible to listen to bats. Single side mod and demod basically.

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Siol
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Reply to
SioL

I suspect going from 10 Hz to 20 Hz, you want something like 120 Hz to 240 Hz, and not 120 Hz to 130 Hz. I was thing maybe a frequency to voltage to frequency setup.

greg

Reply to
GregS

"Jacques St-Pierre"

** A " frequency up-shifter" is the ideal solution.

One that adds a fixed frequency to any incoming complex signal.

It is an analogue circuit, but not exactly simple.

** If you have the time and *where with all* to go snooping on whales at sea with a hydrophone - you can easily pay for a suitable device.

........ Phil

Reply to
Phil Allison

Frequency muliplication and shifting are going to introduce artifacts that will distract you from the signal of interest. My suggestion is to amplitude modulate a white noise "carrier", so you can hear the actual pulsations and time duration of the original signal. You cannot do this with a "simple analog circuit" - it will take some work. I suggest testing the idea first with a computer and a sound editing program.

-- Joe Legris

Reply to
jalegris

This one makes the most sense to me, albeit he wouldn't be able to listen in real-time. Just record it and play it back faster, like they did with the caterpillar drive in "Hunt for Red October". :-)

Cheers! Rich

Reply to
Rich Grise

Here are some other suggestions:

  1. Full wave rectify the signal, without filtering. This will double the frequencies, but will probably still be too low in frequency.

  1. Use the signal to AM modulate a carrier at several hundred Hertz.

  2. FM modulate a carrier.

  1. You would get an undistorted translation of frequencies by generating an upper sideband single sideband signal at , say, 100 Hz. Two problems I see are that you lose the harmonic relationship of the original, and it will get you into a nice filter design issue.

Tam

Reply to
Tam/WB2TT

Reading all the answers, I think this problem calls for a DSP-ish solution. What you need is a vocoder or pitch-shifter. It can shift pitch and / or stretch signals. Code examples are available on internet.

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Reply to
Nico Coesel

That's what I'd do. Use the ENVELOPE of the original signal to AM modulate a carrier.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

"Tam/WB2TT" a écrit dans le message de news:l6KdnSjk0_XuONLZnZ2dnUVZ snipped-for-privacy@comcast.com...

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I think there exist some pitch manipulating software used in studios. The basic idea is that there's lots of redundancy in a sonic messages. So you play it (the message) at several times its original speed, thus keeping its harmonic structure, and keep it's time lenghts by duplicating parts (period lenght) of it, inside the message.

You'll obtain some sort of castrato whale song.

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Thanks,
Fred.
Reply to
Fred Bartoli

It doesn't work that way. Pitch scaling and / or stretching is done by using FFT to determine the frequencies of a signal for a short span of samples. The resulting frequency spectrum is modified and used to build a new signal.

There is some very good in-depth information and source code on dspdimension.com.

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Reply to
Nico Coesel

"Nico Coesel" a écrit dans le message de news: snipped-for-privacy@news.kpnplanet.nl...

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the

generating

I

will

Yes, you're right. I just confused this with what's done in some dictaphones to shorten the playing time without altering the pitch, where they cut some redundancy instead of playing the message faster.

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Thanks,
Fred.
Reply to
Fred Bartoli

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