I am interested in understanding various methods to manage delay compensation (plugin latency) using Ardour as the master mixer.
The goal is to have the ability to determine and control (manually and/or automatically) the amount of delay-compensation induced in certain channels so that certain critical specific components of the mix (processed separately) arrive at the master stereo/surround bus with phase coherency for an audiophile grade level of detail.
Part of the aim would be to consider that in addition to LADSPA plugs, the mix would also utilize VST plugins as well as physical I/O routed via jackd through various other outboard hardware including other dsp based processing systems as well as various analog eq’s and compressors.
The various routings would potentially include post&pre-fader sends, post&pre-fader inserts, send and insert processing loops fed from both original source channels as well as parallel audio group/bus sub-masters where the original set of audio sources is comprised of sound sources recorded simultaneously in an acoustic space with audible bleed from adjacent microphones.
A common example of this mix situation would be the mixing of a recording of an acoustic drum set with the following complement of audio sources on separate channels (as well as the other instrumentation in the song):
-01- KICK INSIDE
-02- KICK OUTSIDE
-06- RACK TOM 1
-07- RACK TOM 2
-08- FLOOR TOM 1
-09- RIDE CYMBAL
-10- CRASH CYMBAL
-11- OVERHEAD L
-12- OVERHEAD R
-13- ROOM 1 L
-14- ROOM 1 R
-15- ROOM 2 L
-16- ROOM 2 R
Each channel has various inserts as needed (Gates, EQ’s, Compression) and is sent to the master stereo bus.
Delay-compensation is applied to each channel as required (depending on the inserts and processing loops) so that the mix of signals at the stereo bus are phase coherent.
In addition to the stereo bus, a post fader send of each channel is sent to an audio subgroup bus. For example Bus 1&2 as a stereo pair.
Bus 1/2 then has an external analog compressor and an EQ inserted and brought back into an Ardour mixer channel and sent to the stereo bus. The level of the drum-subgroup audio is brought up so that it is just under the original mix of drum audio.
In addition to Bus 1/2, several more stereo post-fader drum subgroups are set up which is also post insert from the original source tracks. These are matrixed and remixed to create a L+R and an L-R which can be processed differently then de-matrixed back to a stereo signal which is then sent to the stereo bus like this:
L (+) -> SUMMED = L+R -> [EQ + COMPRESSION] = L+R-PROC R (+) -> L (+) -> SUMMED = L-R -> [EQ + COMPRESSION] = L-R-PROC R (-) ->
Then bussed and mixed so that
L+R (+) -> SUMMED and sent to Stereo Bus L L-R (+) -> L+R (+) -> SUMMED and sent to Stereo Bus R L-R (-) ->
The matrixed/de-matrixed audio is then brought up to the desired level in the stereo bus.
The problem to solve here is how set up the mix so that it is possible to determine and apply delay-compensation so that there is no comb filtering (phase-coherency/latency differences) in the stereo bus between the three groups of mix sources (Original, Sub 1/2, and matrixed/dematrixed).
This is an example and could be applied to various mixing situations with varying levels of complexity and numbers of audio sources and subgroups which must be phase coherent in the stereo bus and because of the signal flow delaying the source tracks causes the rest of the tracks to also be delayed and retain their latency offset.
I appreciate your input, feedback, and postings.