Your examples aren't exactly the same. In your first example, you're actually missing a comma:
I heard his deep, warm voice filling the room.
You need the comma here because both deep and warm describe voice. What kind of voice is it? A voice that is deep and warm.
She was wearing a deep crimson shirt.
No comma here, and also no hyphen; deep describes crimson, and crimson describes shirt. What kind of shirt is it? A crimson shirt. What kind of crimson is it? A deep crimson.
I think '32-bit' being hyphenated is just because it's become a convention to write it that way. If you wrote 32 out as a word, you wouldn't hyphenate:
The thirty-two bit Pentium had a sixty-four bit data bus.
ETA: Upon further research, it seems that in the first example, you can either use the comma or not use the comma; either would be correct. (Source)
I found this example online that illustrates when to use the hyphens. Basically they are used to avoid syntactic ambiguity; when not using the hyphen makes the sentence mean something else, you use the hypen.
Jacob took the well-fatted calf to the riverside.
('well-fatted calf' as in a very plump calf)
Jacob took the well fatted calf to the riverside.
('well fatted calf' could be construed as a 'well' (i.e., healthy) and 'fatted' calf.
In the first example, the 'well-fatted calf' could be ill.)
This is similar to your added example about the well-known actress:
If you do not use a hyphen, you have:
The well known actress accepted her award.
In this case both well and known apply to the actress. This means she is well (not ill) and known. But that's not what you want to say; you want to describe to what degree she is known, and you don't mean to say anything about the state of her health. So you use the hyphen to make well-known into a compound adjective everyone will understand:
The well-known actress accepted her award.
In your deep crimson shirt example you don't have any ambiguity. A shirt cannot be deep, so no one is going to be confused if you don't use the hyphen. We understand inherently that deep applies to crimson and crimson to shirt. So it seems we use the hyphen to make compound adjectives when otherwise the sentence's meaning would change.
If possible, avoid hyphen with prefix (except for self- and post-). However, if the word looks too clumsy, to avoid ambiguity, we use hyphen.
Having said, in your case, I'd prefer mismodeling. Also, prefix with mis generally does not take hyphen.
Please note that in some cases, you must use hyphen with prefix as in with proper noun (ex-president)
Very good information here that shows other examples and rules.
Best Answer
Two words are joined by a hyphen when the collocation occurs in a non-standard context. For instance, we speak of the front end (space, no hyphen) of a car when this acts a noun phrase:
But when we use front end as an attributive, we hyphenate it:
This lets the reader understand that we are speaking of a collision involving the front end rather than an "end collision" (whatever that might be - it has no obvious meaning) at the front.
In the same way, the phrasal verb is always speed up (space, no hyphen) when we use it as a verb:
But if we want to use speed up as a noun, we hyphenate it.
Two words are compounded - stuck together with neither a hyphen nor a space - when the collocation acquires a distinct sense, or the phrase becomes so common that it is felt to be a single word rather than two separate words. For instance, a dead line or dead-line was originally a line around a military prison which a prisoner could be shot for crossing; but when the phrase came to be applied metaphorically to the point by which a project must be completed, and became very common in the sense, it turned into the single word deadline.