How reliably does this work over FM transmission or VoIP? (If it doesn't I would guess and say that you'd have to add some mechanism to detect reliable frequency bands like in existing modems)
In your experience, how reliable is the communication between 2 devices when using speakers and microphone (no cable) at distance ~3 meters? What bandwidth do you typically achieve in such conditions?
Nicely done, I'll note for the readership here that a similar technique works fine at 300 baud across the room using FSK.
Something you might consider is to write a web camera backend for it and use the screen/webcam. That has a lot more bandwidth and has higher SNR as the selector effect of the web camera is so much better than that of a microphone.
FSK across the room? Does that have noise restrictions?
I’ve found all the phase modulation schemes work poorly across the room. DSSS works ok but is very slow. I would be curious how reliable FSK is in that situation.
With 1270Hz/1070Hz you've got over 3 complete cycles to identify the tone at 300 baud, at higher frequency pairs it gets better. The person who wrote it was Tom Lyon at Sun but I bet I could reproduce it with a gnuradio-companion flow graph. That would make it pretty easy for anyone to play with it.
I don't have first hand experience but I believe a big problem with sound channels is multipath propagation/challenging frequency response. FSK naturally deals quite well with those; it's similar to OFDM but more robust due to single carried symbols. You can extend the symbol period as long as you like while using an adequate number. Finally in challenging environments it'd a good idea to use error correction, not just error detection as done here -- you can (in theory) achieve reliable transmission over arbitrarily noisy channels by adding redundancy.
I have experimented with FSK modulation myself and was able to achieve quite reliable transmission across the room [1]. Although the bandwidth is quite low (8-16 B/s), it works most of the time.
Hi, I did try it and it was working quite good when the devices (phone and laptop) were within ~30 cm. After increasing the distance and putting on the TV in the background it wasn't working that well any longer. I tried only the default protocol with audible frequencies (the ultrasound option didn't work, but my phone does not support the ultrasound option with my application too. guess it's hardware limitation).
I am willing to sacrifice bandwidth to achieve better reliability of the communication and I believe I was able to achieve it. Although, I haven't done tests with many other devices/conditions than my own, so my result might be biased.
Using an audio cable (for better SNR), I have managed to achieve and sustain 60kbps for long periods time - so 3MB file should take ~7 minutes to transmit.
The original goal was transmitting ~10kB in a few seconds over an audio cable, so I didn't try to improve the transmission speed much further.
I guess that adding error correction coding will allow increasing the highest possible bit-rate (currently I'm using only CRC-32 for error detection).
I'm just sitting here and staring at this sentence: "The modulated signal rides on a carrier of a given frequency, but the base band signal got no fixed frequency at all. Because of this, we have the possibility to encode the two-dimensional I/Q signal onto the one-dimensional RF signal without losing anything." I may need to sleep on it...
I guess it should also work on MacOS, since it depends on `numpy` [1] and `portaudio19-dev` [2] Debian packages (which should be installable via Pip/Homebrew).
Btw, is there already a handshake and data protocol for the AI calls via voice to a business phone which happens to be received by another AI? So instead of voice call they try to negotiate using data packets and save some time and clarity.
This doesn't seem very useful. If you already have some agreement between between companies over how AIs communicate, you can create a registry for them and skip the handshake. Use http or something.
Awesome project. I used a similar program (minimodem[1]) a while ago to configure Wi-Fi settings via audio [2]. It's great being able to do some basic setting without having a radio connection. Amazon used the same technique in their Dash-Button albeit in the inaudible range [3].
Awesome library! I feel like sound modems don’t get enough attention and carry some “old-tech” stigma from the dialup days, even though they’re fairly different.
Have you tried the Google Nearby library? Do you think that sound modems still have a place now that Bluetooth LE is more of an option?
edit: Also, do you have a browser version I can try?
I didn't try Google Nearby, since I was developing the modem to run on a desktop machine (but later I've created a simple Android app [1], supporting the lowest bit-rate).
Unfortunately, I don't have a working web-based version of my modem...
This is cool and answered a recent itch. I have a pocket operator (po-32) which you can update to play new sounds by using a data over audio protocol. It's really neat. Thanks for sharing.
Would be happy to answer any question.