Re: [BOUNTY - 25 BTC] Audio/Modem-based communication library
Good news, every one 
I have used today a proper audio cable (instead of a headset) to connect between my PC's audio output and input, so the noise went down dramatically.
This way I was able to achieve 36kbps (after ECC) to successfully transmit 64kB.
Note that there is an overhead of ~2 seconds for the training sequence of the modem, so the effective transfer time is ~15 seconds.
The constellations are here: http://i.imgur.com/7kRtJb9.png
Using 36kpbs MODEM throughput, we can transmit 5MB = 40Mb in ~1111 seconds = 18.5 minutes.
I have used today a proper audio cable (instead of a headset) to connect between my PC's audio output and input, so the noise went down dramatically.
This way I was able to achieve 36kbps (after ECC) to successfully transmit 64kB.
Note that there is an overhead of ~2 seconds for the training sequence of the modem, so the effective transfer time is ~15 seconds.
Quote
$ ./test.sh
+ set -e
+ dd if=/dev/urandom of=data.send bs=1024 count=64
64+0 records in
64+0 records out
65536 bytes (66 kB) copied, 0.00955402 s, 6.9 MB/s
+ python send.py
Running MODEM @ 40.0 kbps
Encoded 65536 bytes
$ arecord rx.int16 -q -f S16_LE -c 1 -r 32000
$ aplay tx.int16 -q -f S16_LE -c 1 -r 32000
Took 17.27 seconds
+ python recv.py
2014-07-09 08:38:23,480 INFO Carrier detected at ~58.0 ms @ 1.0 kHz: coherence=100.000%, amplitude=0.402
2014-07-09 08:38:23,483 INFO Carrier starts at 57.500 ms
2014-07-09 08:38:24,058 INFO Prefix OK
2014-07-09 08:38:24,058 INFO Frequency error: -0.02 ppm
2014-07-09 08:38:24,146 INFO 1.0 kHz: Noise sigma=0.0040, SNR=47.9 dB
2014-07-09 08:38:24,235 INFO 2.0 kHz: Noise sigma=0.0034, SNR=49.5 dB
2014-07-09 08:38:24,323 INFO 3.0 kHz: Noise sigma=0.0026, SNR=51.8 dB
2014-07-09 08:38:24,411 INFO 4.0 kHz: Noise sigma=0.0027, SNR=51.4 dB
2014-07-09 08:38:24,500 INFO 5.0 kHz: Noise sigma=0.0032, SNR=50.0 dB
2014-07-09 08:38:24,588 INFO 6.0 kHz: Noise sigma=0.0025, SNR=52.0 dB
2014-07-09 08:38:24,676 INFO 7.0 kHz: Noise sigma=0.0034, SNR=49.4 dB
2014-07-09 08:38:24,765 INFO 8.0 kHz: Noise sigma=0.0042, SNR=47.6 dB
2014-07-09 08:38:24,853 INFO 9.0 kHz: Noise sigma=0.0075, SNR=42.5 dB
2014-07-09 08:38:24,941 INFO 10.0 kHz: Noise sigma=0.0197, SNR=34.1 dB
2014-07-09 08:38:24,941 INFO Demodulation started
2014-07-09 08:38:36,076 INFO Demodulated 616560 bits : 77.070 kB @ 11.134 seconds
2014-07-09 08:38:37,469 INFO Decoded 65.536 kB
+ python errors.py data.recv data.send
0/524288 bit error rate: 0.000%
+ set -e
+ dd if=/dev/urandom of=data.send bs=1024 count=64
64+0 records in
64+0 records out
65536 bytes (66 kB) copied, 0.00955402 s, 6.9 MB/s
+ python send.py
Running MODEM @ 40.0 kbps
Encoded 65536 bytes
$ arecord rx.int16 -q -f S16_LE -c 1 -r 32000
$ aplay tx.int16 -q -f S16_LE -c 1 -r 32000
Took 17.27 seconds
+ python recv.py
2014-07-09 08:38:23,480 INFO Carrier detected at ~58.0 ms @ 1.0 kHz: coherence=100.000%, amplitude=0.402
2014-07-09 08:38:23,483 INFO Carrier starts at 57.500 ms
2014-07-09 08:38:24,058 INFO Prefix OK
2014-07-09 08:38:24,058 INFO Frequency error: -0.02 ppm
2014-07-09 08:38:24,146 INFO 1.0 kHz: Noise sigma=0.0040, SNR=47.9 dB
2014-07-09 08:38:24,235 INFO 2.0 kHz: Noise sigma=0.0034, SNR=49.5 dB
2014-07-09 08:38:24,323 INFO 3.0 kHz: Noise sigma=0.0026, SNR=51.8 dB
2014-07-09 08:38:24,411 INFO 4.0 kHz: Noise sigma=0.0027, SNR=51.4 dB
2014-07-09 08:38:24,500 INFO 5.0 kHz: Noise sigma=0.0032, SNR=50.0 dB
2014-07-09 08:38:24,588 INFO 6.0 kHz: Noise sigma=0.0025, SNR=52.0 dB
2014-07-09 08:38:24,676 INFO 7.0 kHz: Noise sigma=0.0034, SNR=49.4 dB
2014-07-09 08:38:24,765 INFO 8.0 kHz: Noise sigma=0.0042, SNR=47.6 dB
2014-07-09 08:38:24,853 INFO 9.0 kHz: Noise sigma=0.0075, SNR=42.5 dB
2014-07-09 08:38:24,941 INFO 10.0 kHz: Noise sigma=0.0197, SNR=34.1 dB
2014-07-09 08:38:24,941 INFO Demodulation started
2014-07-09 08:38:36,076 INFO Demodulated 616560 bits : 77.070 kB @ 11.134 seconds
2014-07-09 08:38:37,469 INFO Decoded 65.536 kB
+ python errors.py data.recv data.send
0/524288 bit error rate: 0.000%
The constellations are here: http://i.imgur.com/7kRtJb9.png
Using 36kpbs MODEM throughput, we can transmit 5MB = 40Mb in ~1111 seconds = 18.5 minutes.