When you run it it drops you in a shell, from there, you must first export some environment variables:

Code:

```
export LD_LIBRARY_PATH=`pwd`/lib
export PATH=$PATH:`pwd`/bin
export SOX_OPTS="--buffer 4096 -q"
```

Code:

`bin/play -n synth 4 pluck E2`

Code:

```
for n in E2 A2 D3 G3 B3 E4; do
play -n synth 4 pluck $n repeat 2; done
```

Code:

```
alias pause='play -n trim 0.0 0.1 remix - ' # North American Off Hook Signal Gap
pause # I need this because the pandora is silent on the first command!
play -n synth 0.1 sin 697 sin 1209 remix - # Keypad 1 Signal
play -n synth 0.1 sin 697 sin 1336 remix - # Keypad 2 Signal
play -n synth 0.1 sin 697 sin 1477 remix - # Keypad 3 Signal
play -n synth 0.1 sin 697 sin 1633 remix - # Keypad A Signal
play -n synth 0.1 sin 770 sin 1209 remix - # Keypad 4 Signal
play -n synth 0.1 sin 770 sin 1336 remix - # Keypad 5 Signal
play -n synth 0.1 sin 770 sin 1477 remix - # Keypad 6 Signal
play -n synth 0.1 sin 770 sin 1633 remix - # Keypad B Signal
play -n synth 0.1 sin 852 sin 1209 remix - # Keypad 7 Signal
play -n synth 0.1 sin 852 sin 1336 remix - # Keypad 8 Signal
play -n synth 0.1 sin 852 sin 1477 remix - # Keypad 9 Signal
play -n synth 0.1 sin 852 sin 1633 remix - # Keypad C Signal
play -n synth 0.1 sin 941 sin 1209 remix - # Keypad * Signal
play -n synth 0.1 sin 941 sin 1336 remix - # Keypad 0 Signal
play -n synth 0.1 sin 941 sin 1477 remix - # Keypad # Signal
play -n synth 0.1 sin 941 sin 1633 remix - # Keypad D Signal
```

However, I'm trying to reverse it: I get a sound in the microphone, and I want the corresponding letter. In a way, I need some information about how Commodore and spectrum transformed a tape audio into bytes.

So far, I learned that the Goertzel_algorithm is faster than FFT (Fast Fourier Transforms) and there seems to be code available but nothing I can work with at the moment . Does anybody have a shortcut into that? Can SoX do it with FIR or Hilbert commands?