If I type the following at the terminal I get the expected tone.. /usr/bin/padsp /usr/bin/tones sine 100 900 ...but if I try this from within some C code on a R-Pi Zero... system("/usr/bin/padsp /usr/bin/tones sine 100 900"); I get... [tones] Connection refused : /dev/dsp and with -d on... utils/padsp.c: dsp_open() utils/padsp.c: fd_info_new() utils/padsp.c: pa_context_connect() failed: Connection refused utils/padsp.c: freeing fd info (fd=4) utils/padsp.c: Draining. utils/padsp.c: dsp_open() utils/padsp.c: fd_info_new() utils/padsp.c: pa_context_connect() failed: Connection refused utils/padsp.c: freeing fd info (fd=4) utils/padsp.c: Draining. [tones] Connection refused : /dev/dsp Can anyone please put me right ? Thanks, GB.