All:
 
Can someone explain to me the distinction between Multi-band compression and Dynamic EQ in attenuation mode #and# Multi-band expansion and Dynamic EQ in gain mode.
 
I'm conceptually struggling with when to use either or the other .....
 
Thanks
 
-D

The difference is subtle, and 90% of the time either one will do the job.
 
With multi-band compression, you first split the incoming signal into bands using steep filters and then compress each band separately before recombining them. With a dynamic equalizer, there are no steep filters unless you want them, and no need to recombine bands. A dynamic EQ can therefore be more transparent because you avoid issues that are inherent in steep filters.
 
The spectral effect is also different. Dynamic EQ can be more precisely targeted. With a multi-band compressor, all frequencies within a given band are compressed equally. A dynamic EQ can do this too if you want, but alternatively it can also apply the effect to a specific frequency or as a high- or low-shelf.
 
Dynamic EQs can also be used for expansion as well as compression. If you've got a vocal, for example, that lacks bite, a dynamic equalizer can be used to boost the upper-mids only for those phrases in which they're lacking while leaving other phrases alone that already have enough bite.
 
As you can probably guess, I'm a fan of dynamic equalizers. Although either will work 90% of the time, I cannot off the top of my head think of any scenario where a multi-band compressor would do a better job than a dynamic EQ.

Bit is the one to listen to. He has published on the subject.

I have had a dynamic eq for only three days and I may never use a Mbc again. Still getting  used to it, but i can already do what i do with an mbc without the downside issues.

 
I use a multiband dynamics tool which can gate, compress or expand. Although I tend to try use slight eq to boost frequencies in the mix whenever I have the opportunity.
 

Bit (and all):
Thanks for the responses.  A couple things I'd add to the discussion:
 
First, the steep filters in MBC is certainly a distinguishing factor with DEQ.  
 
How about phase linearity in DEQ vs. MBC. It would seem subtle but a distinction none the less.  
 
WRT MultiBand expansion, it would seem DEQ in gain mode would be far more subtle and surgical in application.  
 
And a final thought .... in this comparison context .... what is a de-esser?  is it a DEQ?
 
Thanks in advance.
 
-D
 
 

Traditionally, De-Essing usually meant compression around 2K. I'm sure I'll be corrected if I'm wrong, but that's the old school way. 
 
Since a mono vocal track usually needs de-essing when other sounds aren't occurring, you can achieve the end by sending the vocal to a compressor and a copy of the vocal with EQ cut hard everywhere but what you want reduced (like 2K range) to the side-chain. Then the compressor will trigger when those sounds pass, even if those sounds aren't very loud (because they are loud on the side-chained version). Since the side-chained version doesn't have any mids or lows, it will not compress the vocal during those.
 
The technique has come a long way. There are a million plugins that do it a million different ways. But I think what I describe above counts as old-school de-essing. Now, multiband DEQ is easily done with plugins and certainly does the trick. You can also use a massively multiband compressor. You could still use the side-chain to the massively multiband compressor to get it to pay closer attention to sibilance. 

A de-esser is neither MBC nor DEQ. It is technically a broadband compressor with a bandpass filter in the sidechain.
 
Both multiband compressors and dynamic equalizers can be used for de-essing, but a conventional de-esser is going to be the most transparent in the most common scenario, vocals.
 
In terms of phase linearity, both dynamic EQs and MBCs do effect phase shifts, the former more so than the latter. If that's important in a particular project, that would be one instance where a multiband compressor wins over a dynamic equalizer. However, unless you're doing something wacky, phase shifts won't be enough of a concern to be the deciding factor.
 

I've just discovered MB Compression!  Who knew?  Well, you guys did, but I didn't.  Now I have to go back to the mixes I've done so far and make them sound like they're supposed to:)

Works great on vocals, too, not just the master bus.