HDMI to TTL with isolation
We made this HDMI to TTL interface to improve the transport conditions of i2S and DSD signals. HDMI transport is superior to TTL, in fact TTL should not be used at all outside of chassis. i2S is better than SPDIF as the signals are separated where SPDIF combines them together.
Also included in the interface is a isolator chip (ISO7240) that will keep the ground from HDMI and TTL sides separated. This will prevent ground issues and reduce noise. USB isolators are currently limited to 96kHz sample rates (USB Full speed), so i2S isolation is the only isolator type that can handle high samples rates, up to 384kHz.
The isolator supports 4x signal transmission (i2S or DSD) and 2 x control signal (DSD128 flag and DSD/nPCM flag) isolated by photocoupler (optical isolator).
The TTL connections: