A simple speaker management LV2 plugin with global master volume and per-channel trim, delay, and low-shelf.
This plugin lets you optimize a stereo or multichannel speaker system to your listening environment.
In most real-life rooms, you will not be able to position the speakers according to a perfect stereo triangle or ITU circle. By carefully applying per-channel attenuation and delay, you can restore almost perfect reproduction at the listening spot.
For example: you have a 5.1 system, but your listening sofa is against the back wall, and the surrounds on that same wall. This means they will be louder at your ears and dominate localisation, because their sound will reach you earlier than the LCR speakers. Measure the distance to the speaker that's furthest away from you. This is the delay reference (it gets no delay at all). Say it's the left speaker. Now measure the distance to the centre speaker and compute the distance difference. Say it's 30 cm closer to your listening position. Sound travels 30 cm in one millisecond, so if you delay it by one millisecond, it will arrive in-phase with the left speaker at your ear. The right speaker is 10 cm closer, that means it should get roughly 0.33 ms delay. The surrounds are 3 m closer, so they need 9 ms delay. For 5.1, it is recommended to have them hit another 10ms later than the front, for a total delay of 19 ms (unless your amplifier already does that).
A speaker that is closer is also louder, you can compensate that by ear using the per-channel trims. If you place a speaker next to a wall, this will boost the bass compared to a free-standing speaker by about 3dB. If it's in a room edge, the boost is 6dB. If it's in a room corner, it will be 9 dB. This can be corrected with the per-channel low shelves.
A precise calibration procedure including test tones will be added to this README in due course, which will allow you to align your speakers to a few samples and less than one dB precision just by using the amazing capabilities of the human hearing system.