ultrasonic translation

Hi All,

Is there a way to generate ultrasonic audio translation using Audacity?

A hardware process is described:

“Live voice speech (300 to 3000 Hz) was delivered through a microphone, amplified, and translated into the ultrasonic range. The carrier frequencies used were 28 and 40 kHz. The double side band (DSB) carrier-suppressed signal was filtered with a Kron-Hite model 3750 filter set in high-pass mode with a cutoff frequency of 20 kHz and a slope of 24 dB per octave. This filtered signal was delivered through the Wilcoxon research model PA7C power amplifier and the model N9 matching network to the model F9 piezoelectric vibration generator on a model Z9 transducer base. The accelerometer output of the transducer was used as input to the Quest Electronics measurement instrument, and signal levels were determined. The accelerometer output was also sent to the Hewlett-Packard model 3561A dynamic signal analyzer, allowing the spectral content of the ultrasonic, bone conduction speech signal to be analyzed and monitored. A DSB signal is generated by the multiplication of two input signals, one modulating (audio) signal and one carrier (high-frequency) signal, using a balanced modulator. An upper side band signal was generated by phasing method such that both the audio and the carrier were shifted by 90[degrees], fed into each of two balanced modulators, and summed [F. G. Stremler, An Introduction to Communication Systems (Addison-Wesley, Reading, MA, 1982)].”



Correct me if I’m wrong, but I think this is the same principal as AM radio (it’s been 7 years since that class). If I’m correct it would require these three things:

  1. A file format with the ability to carry at least 50KHz (because they want the upper sideband and are using a 40KHz carrier). A 96KHz sample rate can almost do this, but you’d be left with terrible audio quality. They mention something about a 28KHz carrier frequency, but I don’t think this is a good idea, the shifted audio would still be audible (if the negative frequencies don’t cancel it out, I can’t remember if they would). Both of these carriers are far lower than any AM carrier frequency, but I think the math should work the same.

I suppose a 192KHz file could carry this information.

  1. A way to multiply the signal by the carrier frequency at the right phase angle. Currently Audacity isn’t designed to do anything like this. I have no idea how you would go about finding the right phase angle of the carrier frequency without using trial-and-error. Further, I don’t know much about carrier-suppressed info, but that would make it harder to find the exact frequency needed for the carrier.

  2. A way to accurately filter out the sidebands you don’t need. This would require a pretty complicated filter that Audacity currently doesn’t have (since complicated filters are generally avoided when working with regular audio).

So, at the moment, Audacity can’t generate a file like this. And I’m pretty sure you won’t be able to convince anyone to code for it either.

It might be possible that there is AM radio software out there that would help you, but I’m just guessing.

Can I ask what you’re ultimately trying to do?

Thanks for the reply,

Yes it seems that AM is based on multiplying a wave with a carrier frequency.

(1) Yes the sample rate of the file (file format?) would need to be sufficiently high.

(2) I suppose you’d be able to hear- trial and error- and vary the phase angle accordingly. But the bigger issue is finding the means to multiply the waveforms- any software options?

(3) Filtering of sidebands- I have a feeling that commercial digital sound studioes offer such functions.

And the reason- I’m interested in this stuff- researching this-

“As previously observed [3, 4], humans have ultrasonic hearing, but only when these vibrational stimuli are presented by bone conduction. The present results suggest that some neural substrate is capable of encoding speech signals when these speech signals are modulated into the ultrasonic frequencies. This is true in the normal hearing individual, the older listener with compromised auditory function, as well as in the profoundly deaf person with no substantial auditory function.”
Lenhardt, Martin L., Ruth Skellett, Peter Wang, and Alex M. Clarke. "Human ultrasonic speech perception. " Science. 253.n5015 (July 5, 1991): 82(4)

Next question- is Audacity capable of generating tones in the range 20-90Khz? using the tone generator function?

I’m sure it would require only minor modification, but Audacity cannot currently generate a tone higher than 20KHz.

There’s also no function to multiply two signals, though this would also be very easy to implement.

This sounds like a really great idea. But at the moment, the only software I know of that can do all these things would be something like Matlab and that’s not cheap or easy to use.

I suggest posting this in the “Adding Features to Audacity” forum, the developers tend to hang out there more often. They might not answer right away, so don’t get discouraged. I don’t know how often they check the boards.