DET3-STG SYNC BUS
When we developed the internal sync bus in 2007, it was for the purpose of driving our modular sequencer system. There weren't any sync standards in existence that could convey musically useful information. It was all in Hz or terms of clock pulses instead of bars, beats and ticks. This led us to the use of DIN Sync for internal sync. It's simpler than having to either format-convert or toss around MIDI clock messages, and also has tighter timing when implemented correctly.
The Modular Sync Bus, co-developed by Detachment 3 and STG Soundlabs, is a method used to buffer and distribute standard DIN Sync inside of a modular cabinet. It follows the same voltage and timing specifications of DIN Sync at 24ppqn, and is distributed on a 3-pin MTA-100 header.
DIN Sync was introduced by Roland Corporation in the early 1980s as a mechanism to synchronize their TR series of Rhythm Composers. Since then, it has been included in many different products including synthesizers, sequencers and drum machines. In its simplest form, DIN Sync includes a CLOCK signal which operates at 24ppqn and a START/STOP signal that acts as a gate. When START goes from 0V to 5V, the slave device starts playing from the beginning of their associated sequence or pattern. When START goes from 5V to 0V, it stops.
For a more thorough introduction to DIN Sync, please refer to this Wikipedia entry. It also has links to fully technical descriptions including implementation differences on different hardware. All STG Soundlabs and Detachment 3 Products only support a clock rate of 24ppqn, and we recommend using the same clock rate to simplify configuration and minimize confusion within the modular arena.
In moving DIN sync from the desktop to the modular cabinet, we wanted to preserve the point-to-point nature of the bus. Therefore, we only provided for one DIN sync "source" in a modular system that feeds a distribution network. Connections are not bussed, therefore one output from the distribution board should feed only one input on target modules. The STG Soundlabs Time Buffer is an integrated receiver and buffer that implements this strategy. The panel has a standard 5-pin DIN connection from the outside world that drives the distribution network, with an added 5-pin DIN to send sync back out of the case for larger installations. We have customized these modules for clients that wanted 1/4" or 3.5mm jacks instead of the standard 5-pin DIN arrangement, and also sell the printed circuit assembly for internal-only sync distribution from in-case sequencers. Depending on the buffers used, the distribution boards can be cascaded up to 4 levels deep without any significant delay appreciating. Since each distribution board supports 8 destinations, that allows a minimum of 29 clock slaves to be driven by a single source.
These rules allow a very simple yet very flexible sync system to be installed inside a modular cabinet with a minimum of confusion and complication. Firmware is simplified when designing modules because you are either a master or slave, and connecting modules is also very straightforward and low-effort in most cases.
In our distribution of DIN sync internally, we simply re-buffer the START/STOP and CLOCK signals and send them over the MTA-100 headers. Our pinout is shown in the following image:
To keep level translators to a minimum, we used 5V TTL signaling levels. We're also providing a copy of our V1 Time Buffer schematic for a complete implementation reference.