Multiband compressor and 4 band EQ on final PA mix?

Discussion in 'Location Recording' started by GxL, Jan 13, 2009.

  1. GxL

    GxL Guest

    Hi folks,
    In a few days I'm going to do a PA mixing of a higher profile concert event and therefore I am looking at further improving my PA mix sound.

    I was thinking to use Multiband compressor and 4 band parametric Eq (software based) with real-time freq. analyser for tonal touch ups (and maybe Limiter) on the output of my PA console.
    FYI the 4 band EQ is NOT for room and speaker equalisation - that is taken care of separately.

    The dilemma I'm in is that a friend of mine argues that nobody uses multiband compression on live mixes, only in mastering studios. He argues that for live mixing only straight full band compression should be used. I, on the other hand, see no reason (maybe due to my limited experience) why multiband compression should be wrong on PA final out. I would think that it is always better when it comes to mixed-down live music to have the freq. bands handled separately.

    Maybe he's right about not using multiband compression but I would like to hear it from more people (experts) and also why.

    Any opinion and experience would be highly appreciated.
    What are your experiences and views?
    Thanks in advance
    GxL
     
  2. RemyRAD

    RemyRAD Well-Known Member

    You are going through a gear fetish. Your friend is absolutely correct. Mollified band compression is not intended for PA purposes. It only helps to cause hideous feedback problems. It's much more applicable to broadcast transmitter limiter, Dolby like spectral processing. In fact the only thing you should have on the output of your mixer is a fast acting, wide band limiter. That's all. Lots of compression & P. A. absolutely do not go together. What do you not understand about controlling feedback? Compressors keep turning things up. You definitely don't want that. You just want a limiter on your output. And I wouldn't be experimenting with a recording such as this. Best to go with people who are in the know. But go ahead and make your mistakes. You can then stand their scratching your head wondering why it didn't sound good?

    You don't see any problem because you don't know what you're doing. You think it should be OK but you really don't understand multi-band compression. If you did, you know it's inappropriate for PA applications. you have this idea in your head how it should work & sound. It won't sound that way. In fact, you may not even be able to turn the PA system up to its proper level.

    It's no problem getting into a Ferrari & driving as fast as it can go. You probably won't live long but it stands to reason that you could drive it as fast as you want.

    So now you've heard another person tell you why you shouldn't play with a multi-band compressor for PA applications. Not all audio equipment is intended to be used in all audio situations. This comes from experience which you need.

    I wouldn't see any problem running my equipment at 220 volts instead of 110 volts? I think it would make everything sound twice as good. It will provide more output level. Sounds like a good idea doesn't it?

    Old fool
    Ms. Remy Ann David
     
  3. GxL

    GxL Guest

    Thanks Remy,
    ...wow, you shot me down in flames with a few wrong assumptions.
    I was expecting a bit friendlier folks here - not calling me or anyone "old fool" without giving a reason... :-(

    Firstly i was intending to use max 3-4dB gain reduction on all bands - not heavy compression as you assumed which would lead to a feedback hell. As I mentioned in my first message I don't claim huge experience but have a few years up my sleeves) and therefore I'm asking here. So far no body said that I didn't know what I was doing. It was the opposite - from all the gigs I had only the most positive feedback from people who know.
    I do now how compressors and multiband compressors work (in fact I have designed one too for your record) but I have never used one on live mix.

    The friend of mine has got much less experience than I do and that was the reason I was going for a forum of experienced pro's to see what they've got to say. Would you not do the same?

    I am interested very much in experienced peoples views but not their arrogance (sorry but that's how you came across to me). Some of the analogies you used are somewhat pathetic - like the 220V on 110V devices.
    However, back to the topic - if that's how it is, what you said that the Multiband EQ is a big "NO-NO" I'll take it - no argument here from me. I'm not a stubborn teenager who would try to prove the opposite of what others have painstakingly discovered.

    Thanks a lot
     
  4. Boswell

    Boswell Moderator Distinguished Member

    The general rule for live PA work is minimal (if any) compression, mainly to avoid feedback problems. It's better if you can to use the compressor as a limiter, so that it's normally running in its linear gain region and only kicks in if there is an unexpected transient. If you must use compression, consider using it only on the necessary input channels and not on the stereo FOH mix.

    Multiband compression for PA use is by extension a non-starter. It's essentially a mastering tool that can also be employed carefully in post-production mixing for de-essing and other specific tasks. It usually takes many passes of listening to the results to get the multiband parameters set correctly, and this is a luxury you just don't have with live sound.

    Software EQ should be avoided for live use purely because of the delays (latency) involved. Live sound is about the only instance where I use a 31-band graphic (analog) EQ, but its use is to match the loudspeaker system to the acoustic of the venue, not to compensate for frequency-related problems in the live mix.
     
  5. GxL

    GxL Guest

    Thanks Boswell for your well put answer.

    I must say I haven't realised one of your very strong point about the luxury of multipass listening in studio conditions. I can see that.
    The truth is I have never used any compression on FOH mix signal or tone shaping EQing. And that, what you're saying was my understanding all along before. When a friend of mine used full band compression on a final mix I though of it as a flawed idea. I see that my thought was even more flawed.

    Thank you very much for well explained reasons - I appreciate it very much.
     
  6. Cucco

    Cucco Distinguished Member

    Also...
    Do me a huge favor and go smack your friend upside the back of his head. That would be for advising you that Multi-Band Compression is for mastering...

    I don't know of any serious mastering engineers that use them. Most ME's abhor them - mainly "ghetto" mastering houses use them to make things "LOUDER!!!"

    Cheers-
    J

    PS - Oh...and Boz is right on everything else...
    :)
     
  7. Codemonkey

    Codemonkey Well-Known Member

    Speaking of multiband stuff...

    IQ4Gui is a multiband compressor with a difference - it doesn't adjust gain envelopes. The detector controls the amount of gain given to a parametric EQ.

    It's an excellent free plugin IMO.
     
  8. diablo

    diablo Guest

    A limiter is the only compression I'd use on the outs and that's for speaker protection. You'll be chasing your tail all night with compressors across the left and rights.

    By all mean use compression on individual channels. I tend to use a mix of comps on individual channels and on subgroups, eg kick and snare subbed together and lightly compressed, but that's as much to do with keeping the number of dynamics to a minimum and having less things to have to fiddle with!

    Parametric EQ - nice to have a good analog unit in the FOH rack, but more of a luxury than a necessity; a good graphic will sort most issues. Software based stuff scares the bejaysus out of me!
     
  9. RemyRAD

    RemyRAD Well-Known Member

    On a few occasions that I do live PA sound, I'll put individual broadband compressor/limiters I'm certain instruments & vocalists. But they really don't get turned up much. You can't. So it's mostly just for limiting transients on a one-on-one level. Not overall.

    Multiband compression actually became popular with TV & FM & AM. radio & Dolby A/SR noise reduction. Few people know that a Dolby A 361 makes for a dynamite studio multiband compressor, complete with smooth downward expansion. Nope. You don't always need to encode & then, decode, when used in that kind of an application. That's not noise reduction but spectrally defined compression.

    You just can't engineer for live PA like you can in a recording studio control room.

    I don't usually accept PA work. I like my hearing.
    Ms. Remy Ann David
     
  10. IIRs

    IIRs Well-Known Member

    Remy is correct: for live sound you will mostly just need broadband compressors on specific channels. How much compression you can use will depend mostly on the source: if you have a singer with a very powerful voice you will probably be able to compress it pretty hard. If your singer is barely whipering however, you will probably not be able to use any compression at all.

    I have seen live engineers use compressors (or other processors) inserted into the mix bus however. Usually it will be some nice valve compressor, or sometimes an XTA SIDD to add some artificial valve type harmonics; I never saw anyone use a multi-band.

    Groups are another interesting place to put compressors, especially if you double route: try routing your kick and toms (for example) to a sub-group as well as direct to mix, then compress that group pretty hard and mix that in to taste. This trick can fatten drums, or add punch, and does so very transparently without killing the transients or squashing the sound at all. (Just be careful of latency if you try this with a digital desk, or digital compressors like the XTA C2)

    In fact, multiple parallel compressors might be a better alternative to your mutli-band compressor idea, eg: set up 3 comps on 3 groups, then send (say) kick, toms and bass guitar to group 1, snare and electric guitar to group 2, and keys and acoustic gtr to group 3. You can then use the group faders to control the amount of resulting 'upward compression' applied to each section of the mix, and can add some of the punch and fatness of a good studio mix without killing the dynamics or risking unpredictable feedback on the vocal mics.

    Yeah... you don't need to work to make thigs "LOUDER" when you have a good PA system. On the contrary, you should aim to give the audience the excitement of a wide dynamic range, which is something they don't experience when listening to smashed modern masters on ipod earbuds.

    Thanks, glad you like it. :D I actually find dynamic EQs very useful for live sound. Hardware ones obviously, such as the BSS DPR-901: they can work wonders for singers with tricky voices, or acoustic guitar DIs, and probably a load of other stuff too... I wish I had a hardware IQ4!

    Thinking about it, I have seen someone use a dynamic EQ over a whole live mix. Can't remember who it was, but he was using an XTA D2 to compress the 700Hz region, quite heavily from what I could see from the meters. I don't think he was applying any make-up, so it was only ever subtractive EQ, and it was kicking in mostly on the vocals in the choruses as far as I remember. Thats the closest I ever saw to the OP's suggestion.

    Hmm... actually the current trend is towards ever more draconian noise limits, especially at festivals. I've seen punters begging the FOH engineer to turn it up just a little bit, while he shrugs and points at the man with the meter. I was threatened with a $30,000 AUD fine at the same gig (me personally that is, not the band or the production company) if I didn't turn it down immediately... this was in the last minute of the last song of the set, when everything built up to a climax (and I told him that) but he still made me back it off by about 6dB.

    I totally agree that it shouldn't be too loud, but I thought that was a bit extreme. :?
     
  11. GxL

    GxL Guest

    Thanks, IIRs, for your very specific tips - absolutely fantastic.

    I will endeavour to try out some of your tips off line but first I will have to work out how I could achieve some of them on D-Show Profile console - it's got its limitations but still fairly powerful.

    I really appreciate your tips and tricks.
    I have a simple question while I'm here for my own benefit. I have heard of dynamic EQs but never looked closer as to how they work.
    Are they the kinds of parametric EQs where you can set (as with ordinary param. EQs) the freq, Q, and gain, but also some input level threshold at which the EQ's gain adjustment kicks in? So if the gain is set to -ve then at and above the threshold level the EQ would start suppressing the set frequency area or if gain set to +ve it would conversely start boosting the specific frequency area?
    If so, isn't it also something that would require a lot of careful fiddling to set it up correctly (similar to what Boswell above described) which is really not practical for live mixes? Perhaps we are talking about small gain adjustment like no more than +-3-4dB? Or how far it is practically manageable to push the EQ's gain? Just interested in your experiences.

    Thanks so much for sharing your experience (that goes for all the posters above as well)
     
  12. GxL

    GxL Guest

    Just to clarify my dynamic EQ gain related question, I would imagine that in live production (channels or groups level) one would really NOT use +ve gains as that could cause real feedback problems and get out of control, right?
    ...rather subtractive EQing (-ve gains)?
     
  13. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Try going to the BSS Audio website and check out their 901 and other dynamics processors...
     
  14. IIRs

    IIRs Well-Known Member

    I quite like the D-Show stuff. The parallel compression is set up the same way it would be on an analog desk: simply route your channels to a subgroup as well as to L+R, and make sure the subgroup is also routed to L+R. You will need to use a plug-in to provide the compression, and will also need to switch the delay compensation setting to "Mix & Inserts" (Options -> Pickoffs -> Delay Compensation) otherwise you wil get comb-filtering when you turn up the groups.

    I'm not aware of any dynamic EQ plugins for the D-Show. I would have found one really useful on my last tour actually: I had to use a BSS unit instead. (I wired it in-line after an Avalon pre-amp rather than patch it as an insert, so I didn't get any extra latency).

    One useful option on the D-Show desks is the side-chain filtering for the dynamics. I will often high-pass filter the compressor sidechain quite severely on sources such as trumpet, so the compressor will effectively have a lower threshold for high notes than for low: the trumpet might be audible without a mic at all when played up high, but need more re-inforcement when played in a lower register.

    Start off by imagining a normal full-band compressor, with a narrow band-pass filter inserted in the side-chain: the compressor will turn down the whole signal when the threshold is exceeded, but will react only to frequencies at or near the filter's center frequency. Now imagine that the side-chain controls the gain of an EQ circuit instead of a conventional VCA: if the frequency of the EQ band is set the same as the side-chain filter you will be able to compress just that specific frequency, and can do so much more precisely and surgically than you could with a multi-band compressor.

    ;)

    Depends what you are trying to do. The BSS DPR-901 is much simpler than my plug-in, which reduces the options somewhat.... last tme I used one I basically only used one band. I set it to approx. 2KHz and used it to control the region that would otherwise get harsh when a particularly challenging singer I was working with switched to her higher register. The gain reduction was pretty extreme at times (9 to 12 dB perhaps?) but there was no boosting, only cutting (the 901 has no "make-up gain" for the EQ as does my plug). It worked very well, much better than any compressor I had tried. But she has a very unusual voice, that sort of extreme processing should not normally be needed.
     
  15. Codemonkey

    Codemonkey Well-Known Member

    Quote (IIRS):
    "Codemonkey: (something)
    Glad you like it :D"

    You made IQ4gui?
     
  16. GxL

    GxL Guest

    I had the same question on my mind... :D
     
  17. Codemonkey

    Codemonkey Well-Known Member

    Oh, I skipped a post.
    Question answered. However, I feel the need to say to IIRS...

    You Sir, are Awesome.

    However, I have a bug to report. It may or may not be related to Kristal though, the same happens when it's in being hosted in multiFXVst.
    Related to the Window being closed (plugin still active) then reopened - you need to de/reactivate the plugin before the display updates.
     
  18. GxL

    GxL Guest

    I had the same question on my mind... :D

    ...and then I read:

     
  19. IIRs

    IIRs Well-Known Member

    Yes, but the gui was from http://www.novaflash.com (the original "IQ4" looked like a child's toy!)
     
  20. IIRs

    IIRs Well-Known Member

    I think I've seen that one in Tracktion. I believe its an issue with one of Synthedit's graphics modules...

    Its quite a long time since I used IQ4 however, as I have been working on a new version... its not ready for release yet. (God knows when it will be: I will have to sell it not give it away because it uses custom made modules for which I promised the developer a cut, but that means it needs presets and a manual and a website, and I just don't seem to have the time.:( )
     

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