After a lot of time with this game I’ve only just realised some fundamental, critical mechanics with Chanters. The game makes no effort to explain them to you, so I expect many people are as clueless as I have been all this time. This is something I’ve only just discovered so I expect I will have a lot to learn from others in this thread who are more familiar with this.
This is what I’ve found playing a Skald/Helwalker with the chants Ancient Memory (hereafter AM), The Fox from the Farmer (FF), and The Dragon Thrashed (DT). I’m using the Deadfire Polishing mod and Community Patch (they buff the latter two)
Let me itemise the key points to make this more digestible:
1) For at least the chants listed above, what happens is that at the beginning of the phrase, an effect is applied to allies (for AM) or enemies (for the others). The duration of these effects is your 6s +3s linger, and the linger only is affected by INT. AM will always have this same duration, but chants which perform an attack roll like FF and DT have their duration modified by whether they graze, hit, or crit.
2) Once the effect is applied, nothing the chanter does affects it (with the exception of re-applying it). This means that you can start combat, begin chanting AM, then immediately switch chants to FF and, once FF hits (or grazes, or crits), both AM and FF will apply their full effects for their full durations. So, you can have two (or more) full-fledged phrases active within about a second of each other. The only penalty for this is that you only accumulate phrases (the resource used for invocations) when your chanting of a phrase naturally elapses – so switching your chants over and over again will mean that you never accumulate phrases. That aside, you can just cycle through four chants whenever you want and enjoy the benefits of all of them one after the other. Note, though, that there is an unchangeable cooldown on chant switching whenever you start a new chant. I now realise that this exists so that you can’t have the full effects of four phrases going instantly – it will at least take you a few seconds to cycle through them (but you can have four active at once – easily).
3) Casting an invocation does not only pause your chant progression, it resets it. Let’s say your chant progression is AM->FF->DT. You start combat and begin to chant AM: the effect is applied to you and your team for, let’s say, a 10s duration. If you cast an invocation three seconds into the fight, your chant progression will pause for a second, and then it will completely reset. So, you will start chanting AM again from the beginning, resetting its duration to every ally in range. This means that if you cast invocations quickly one after the other within six seconds of each other (easy for Skald) you will never benefit from more than a single phrase. It also means that if you cast an invocation when you are chanting your second phrase (FF in the progression above), you will go back to chanting your first phrase and not get a chance to chant your third unless you refrain from casting or switching chants for a further 12s! So in our example progression, you will never see DT get applied once you are casting invocations every 12s (I started noticing this weird stuff when I realised that my Skald’s third chant never seemed to get applied unless I sat around waiting for it). This is especially a problem for Skalds because they have powerful invocations that cost only 2 phrases. Other chanters usually need to get 3 phrases to cast their cheapest invocations and so should theoretically cycle through 3 chants when waiting for them. Brilliant, Sasha's Singing Scimitar, and the Weyc's Robes all have obvious implications here as well.
Point (2) makes chanting much more dynamic than I originally thought. You can basically chose what chant you want to apply at any instant with the sole penalty of slowing down your accumulation of phrases. Point (3) can be incredibly frustrating, but it can also be used to your advantage if you play smart and use point (2) to your advantage. If your chanter can cast invocations quickly, what you should do is wait until you begin chanting at least the second phrase in your list. After you cast, your chant will restart from the first phrase. The restarting process takes less than 6s, so if there are only two phrases in your chant, you will actually have saved time by resetting the chant. Note that casting an invocation will always slow down your accumulation of more phrases but it will slow it down more the longer you wait to cast after you BEGIN to chant a phrase. For example, if you let a phrase go on for 4s and then cast, those 4s will be lost on the reset (they didn’t help you accumulate another resource-phrase). Ideally, you should always cast an invocation at the very instant that you begin to chant a phrase.
Maybe I’m late to the party but I had no idea chanting worked this way. It’s partly exciting because chanting is much more dynamic than I thought before, but it’s also quite finnicky and odd.