Let's break down exactly what's happening here. The sox command accepts an input file and an output file, in that order, together with a myriad of optional parameters. In this case, -t alsa plughw:1 is the input file and -d is the output file. -t alsa plughw:1 means ALSA card number one and -d means default ALSA card, which is the Raspberry Pi sound core. The status line that is continuously updated while sox is running provides many helpful pieces of information, starting from the left-hand side