Question

How can I continue an existing wav recording using SOX ?

I tried with:
rec test.wav –combine concatenate test2.wav

test.wav is the old file
test2.wav is the new file

The problem is that the new recording is placed at start instead that at end of test.wav

Answer 1

The rec command is just a shortcut for sox -d where -d can be used in place of an input or output file to select the default device as input or output. When you write

rec test.wav --combine concatenate test2.wav

it will be the same as

sox -d test.wav --combine concatenate test2.wav

in this case -d is listed before test.wav and thus will be the first part of the output file. Running

sox test.wav -d --combine concatenate test2.wav

should do what you want.