{"id":14612,"date":"2017-12-19T22:20:46","date_gmt":"2017-12-20T03:20:46","guid":{"rendered":"http:\/\/scruss.com\/blog\/?p=14612"},"modified":"2026-05-25T09:22:04","modified_gmt":"2026-05-25T13:22:04","slug":"synthesizing-simple-chords-with-sox","status":"publish","type":"post","link":"https:\/\/scruss.com\/blog\/2017\/12\/19\/synthesizing-simple-chords-with-sox\/","title":{"rendered":"Synthesizing simple chords with sox"},"content":{"rendered":"\n

SoX<\/a> (now typically sox_ng<\/a>) can do almost anything with audio files \u2014 including synthesize audio from scratch. Unfortunately, SoX\u2019s syntax is more than a bit hard to follow, and the manual page isn\u2019t the most clear. But there is one example in the manual that gives a glimpse of what SoX can do:<\/p>\n\n\n\n

play -n synth pl G2 pl B2 pl D3 pl G3 pl D4 pl G4 \\ \n     delay 0 .05 .1 .15 .2 .25 remix - fade 0 4 .1 norm -1\n<\/pre>\n\n\n\n
While it plays a nice chord, it’s not obvious how to make audio files from this process. I have a project coming up that needs a few simple guitar chords, and with much trial and error I got SoX to spit out audio files. Here’s what I keyed into the shell:<\/p>\n\n\n
\ncat guitar.txt | while read chord foo first third fifth\ndo\necho "$chord" :\nsox -n \\\n-r 16000 -b 16 "chord-${chord}.wav" \\\nsynth pl "$first" pl "$third" pl "$fifth" \\\ndelay 0 .05 .1 \\\nremix - \\\nfade 0 1 .095 \\\nnorm -1\ndone\n<\/pre>\n\n\n\n
with these lines in the file \u201cguitar.txt\u201d<\/p>\n\n\n\n
G   :  G2  B2  D3\nC   :  C3  E3  G4\nD   :  D3  F#4 A3\nF   :  F3  A3  C4\nA   :  A3  C#4 E4\nE   :  E2  G#3 B3\nEm  :  E2  G3  B3\n<\/pre>\n\n\n\n
How the SoX command line breaks down:<\/p>\n\n\n\n
    \n
  • -n<\/strong> \u2014use no input file: SoX is going to generate the audio itself <\/li>\n\n\n\n
  • -r 16000 -b 16 \u201cchord-${chord}.wav\u201d<\/strong> \u2014 with a sample rate of 16 kHz and 16-bits per sample, write to the output file \u201cchord-\u2026.wav\u201d <\/li>\n\n\n\n
  • synth pl \u201c$first\u201d pl \u201c$third\u201d pl \u201c$fifth\u201d<\/strong> \u2014synthesize three plucked tones read from the file <\/li>\n\n\n\n
  • delay 0 .05 .1<\/strong> \u2014delay the second tone 0.05 s after the first and likewise the third after the second. This simulates the striking of guitar strings very slightly apart. <\/li>\n\n\n\n
  • remix \u2013<\/strong> \u2014mix the tones in an internal pipe to the output <\/li>\n\n\n\n
  • fade 0 1 .095<\/strong> \u2014fade the audio smoothly down to nothing in 1 s <\/li>\n\n\n\n
  • norm -1<\/strong> \u2014normalize the volume to -1 dB.<\/li>\n<\/ul>\n\n\n\n
    The chords don’t sound great: they’re played on only three strings, so they sound very sparse. As my application will be playing these through a tiny MEMS speaker, I don’t think anyone will notice.<\/p>\n\n\n\n