Soundlink, also known as "Live Voice" and various other aliases, is a Satellaview function in which Streaming Satellite Radio from St.GIGA is played at the same time as software data is broadcast, downloaded and played. This is intended to give the illusion of a game being played with high-quality audio. This was a selling feature of the Satellaview and was used in a lot of it's software.
Soundlink is not emulated on any emulator because no source audio has been dumped or archived (cleanly - there are instances of Japanese fan-recordings of gameplay with Soundlink) otherwise - ROM dumps of games or programs that used Soundlink are often mute or only have sound effects without music, or one or two small jingles.
Method of operation
After being separated from the bitstream data input into the satellaview add-on by the DCD-BSA IC, the PCM data is decoded by the Matsushita MN88821 PCM decoder Integrated Circuit present on the main Printed Circuit board, and then mixed in with the game soundtrack by the SFC's APU. Since the MN88821's datasheet has been lost, it remains unknown whether games could disable Soundlink at will or whether it was a passive addition to the games. However, the datasheet of MN88831, which is similar in function to the one used in the Satellaview main board, shows that the IC can be controlled via three-wire SPI, a claim that is also supported by patent no. 3615588, which mentions that the PCM decoder can be controlled via software by means of a three-wire serial bus.
Citations
Patent no. 3615588 -- Paragraphs 0024, 0034, figures 5, 13
Patent no. 3738857 -- Figure 3