i’m aiming to insert external compressors, eqs or saturation hardware into busses .
This results in a delay of 0.25ms per external insert. This might not sound too much, but it will create phasing issues if send the tracks of this bus also into another bus or the master. (for example to create a dry/wet if the ext. hardware doesn’t offer this)
It should be possible to automatically latency compensate for that, since latency of hardwareinserts is known.
A&H is rightly proud of its overall latency of around 0.7ms, and I fear you won’t want to increase it.
But how do you arrive at your value of 0.25ms?
You can’t “hear” a .25ms delay (you won’t hear a “flam” effect), but you absolutely can hear the effects of the phasing that occurs when two identical audio signals with a .25ms difference between them interact. That’s because the first is a time based effect that happens too quickly to register in our brains, but the phasing caused by the delay literally changes the physical characteristics of the audio waves we interpret as sound, so the overall tone of the audio will be different when phasing is occuring.
So yes, if you are sending a drum buss through some external processing that adds .25ms latency and you have an identical drum buss that isn’t getting the insert treatment also going to the same destination/output, then you want to add a .25ms delay on the buss without the inserts which will bring both audio paths back into “time alignment”. Luckily most A&H consoles have a “delay” setting for each of it’s channels & busses that you can use to make these types of adjustments.
That being said, I don’t think you need to worry about delaying every mic that might have some drum bleed in it (vocal mics for example) because the audio from those mics are so non-correlated from the drum buss that any phasing will be minimal (any EQ on the vocal channel probably creates more phasing than the drum bleed does).
Long story short, make sure you time align identical audio sources with different processing/latency times and don’t worry about matching the total latency times of non-identical audio sources.
There are more ways to keep in mind.
A hardware insert can be at the console’s sockets, at a stage box, at an external converter, with the USB connection and with audio networking connections.
And the latency depends on some other things too.
You need to measure every possible connection. To calculate it with theoretical assumptions would not suffice.