Solid State Music or SSM as they were often called, were known as the "Blue S-100 boards" company.  Their boards were blue colored and while a few other S-100 board manufactures from time to time used boards of this colored material, SSM really made a point of using that material.
 
SSM was/is well known in the electronic music community for their voltage-controlled oscillators, filters, amplifiers, envelope generators, and so on, all of which were implemented on chips (previously synth circuits were discrete-component designs). The rise of SSM coincided with the first uses of microprocessors in synthesizer keyboards and other music gear like drum machines; early computer-controlled analog synthesizers like the Sequential Circuits Prophet 5, for example (which, I believe, used a Z80 processor), utilized SSM chips for the actual sound production. (The Kawai K3 synth from 1985 has SSM chips in it as well.) SSM chips are still used in some new synth eqipment, like some of Doepfer's line of synthesizer modules which are marketed specifically for the distinctive "SSM sound".

The company was located in Santa Clara initially and later San Jose , CA.  They started in the S-100 bus business like most by supplying static RAM cards, but their claim to fame was their early video display card, their VB1A.  It was a very reliable and popular video display card in the early days of the S-100 bus. Many early memory mapped video games were run from either this card or the Processor Technology VDM-1.  Another great thing about SSM Boards was they wrote great construction manuals. Also they went into the theory of the board often with signal profiles.

There is some mention on the web of a "Solid State Music System Sound Synthesizer Card"  where five SB-1 synthesizer cards plugged into an S-100 microcomputer with 32K RAM. Each card provides one channel of music, with control over the envelope and waveform shape, volume, and pitch of the note played over an 8-octave range. Music for the SB-1 is written in MUS-X1, which allows high-level control of the SB-1's special features and simplified encoding of the music. The MUS-X1 interpreter was also able to play “inverted” music from a normally encoded song. Unfortunately that is all the information I have.
  
If anybody has more information about this company pleased let me know. I will be please to share it for all to appreciate.