The SPX file format is a compressed audio format designed for speech. It is Open Source thus can be used for free. It compresses voices at 2 to 44 kbps and supports 8 kHz, 16 kHz, and 32 kHz compression in the same bitstream.
Convert spx with:
|Encoderen.nl|| (3 votes, average: 2.67 out of 5, rated)
|Free Studio Manager (DVDVideoSoft)|| (4 votes, average: 3.75 out of 5, rated)
|Media.io|| (3 votes, average: 4.33 out of 5, rated)
|Switch Audio File Converter|| (20 votes, average: 2.50 out of 5, rated)