## Restating project goals ## I want to design and implement an audio time code (and accompanying hardware) for automated video synchronization, _cheaper than existing solutions_ and working on camera _without sound input_ , using off the shelf components. [[CANONacousticSmall.jpg:pic]] ## Acoustic coupling challenges ## I want to localize pulses at the highest possible precision in the recorded audio. Typical cameras use a sampling frequency of 48 kHz so I'm aiming at a maximum variation of more or less 4-5 sampling periods, ie ±100 μs. For now I'm still exploring which pulse shaping is better at avoiding transients in the recorings. ### Fighting against the camera automatic gain control ### I generate this symmetrical shape from the SAMD21 DAC output and feed it to a small headphone speaker: [[sinx.jpg:pic]] And here's the resulting soud recording, note the asymmetry now present: [[syncbipextract.png:pic]] I guess I should slow down the attack to avoid triggering the AGC too heavily, and generate an already odd signal ([odd vs pair](https://en.wikipedia.org/wiki/Even_and_odd_functions#Odd_functions)). Something like a [tri-level sync pulse](https://en.wikipedia.org/wiki/Tri-level_sync) and try to detect the zero-crossing.