https://en.wikipedia.org/wiki/Quindar_tones
intro tone
ffmpeg -f lavfi -i "sine=frequency=2525:duration=0.25:sample_rate=8000" -ab 8k -ac 1 -codec:a pcm_mulaw intro.wavoutro tone
ffmpeg -f lavfi -i "sine=frequency=2475:duration=0.25:sample_rate=8000" -ab 8k -ac 1 -codec:a pcm_mulaw outro.wav