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Noise floor when recording off the board

Discussion in 'Sound, Music, and Intercom' started by jkowtko, Aug 4, 2008.

  1. jkowtko

    jkowtko Active Member

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    I recently acquired a Soundcraft LX7-32 (original series) and have been working through the gain structure to get the noise floor down on board recordings. I'd like to run this by you guys to see if I'm missing anything.

    * 32 channel board, we ran 12 mics, reveb return, 6 channels band, 2 channels sound effects

    * I muted all other channels to minimize noise through the summing amps.

    * The (5.1 arrangement) speaker outputs are through the four groups and two auxes.

    * I recorded stereo off the LR main outs, through a DBX266xl compressor, and input my Marantz PMD660 line input

    * Originally I sent Groups 1/2 (the LF/RF speakers) to Mix, but I noticed the additional noise floor so instead I routed all input channels directly to mix, which cut down the noise somewhat.

    * I also noticed that with LR a full fader (0) there is noticably more noise than if I drop it to -10 or more. So one correction I made was to turn down all PA speaker outputs 10db, forcing the sound op to push the inputs up another 10db across the board, thereby allowing me to lower the Mix fader down so I would get less noise into the recording.

    * I also checked cabling from LR outs through the compressor and into the recorder ... there was some noise there but it was less of an issue than the board noise.

    The problem I am having IS NOT overall volume or noise through the PA, or recording songs where the volume levels are up. That sounds just fine and I seem to have plenty of leeway on where I can set Group and Mix fader levels.

    The problem I AM having is recording during low level dialogue passages. Since the theater is so small we pull down the reinforcement to the -20 to -30 level during dialogue because you can hear the actors directly pretty well, and at this point we're only adding a small amount of ambient fill. This is where the noise level is noticable. It would also be nice if I could get it nice and quiet during pauses in the music.

    So up to now my take is that you have to keep the input faders as close to zero as possible to get a nice hot signal going into the mix bus, and therefore minimize mix bus noise. Am I on track or is there something else I should be trying?

    Also, can anyone comment on noise floors of the analog boards in general? I had assuming that even a baby Soundcraft should sound a lot cleaner than our old Mackie CFX ... but do I need to move up to a higher end board to get cleaner mixes? Or will they all have the same general issue (in which case I'm thinking digital is the only way to lick this for sure)?

    Thanks. John
     
  2. avare

    avare Active Member

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    It sounds like (no pun intended) that you are taking a recording of the live board mix, which is adjusted for the live sound requirements. Try either:

    a) set up the mix on the group busses and record from those while feeding the busses to the LR busses and adjust the house level from the LR busses, or

    b) run a separate recording mix off the aux busses fed pre fader, so that any changes made on the LR busses have no effect on the recording level.

    Good luck!
    Andre
     
  3. DaveySimps

    DaveySimps CBMod CB Mods Premium Member

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    We have exactly the same board in one of our spaces. I have expirenced some of the issues you have, but not nearly as drastic. As a whole the board is a bit noisier than I expected, but we have never had any evidence of it in recordings (we record 50 concerts a year). I have only on a few occasions had to compensate by running the board harder to improve the over all quality, but that is rare.

    We use 2 aux sends to record directly to a TEAC CD recorder, and have never had a problem with the noise floor there. In fact, we regularly get compliment on how good they sound.

    ~Dave
     
  4. jkowtko

    jkowtko Active Member

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    When the input volume is reasonable it sounds very good, crisp, clean. Just when the inputs are very low, you're stuck listening to the noise floor. It's a fairly low noise floor, but it's still noticable.

    And, yes, when I personally mix the show and am recording that night, I always push the dialogue a bit high to make sure the recording picks it up well.

    And, I do have the PA outputs on separate busses, so last night I dropped the PA outputs to force the sound op to run all inputs higher, and that helped.

    I have noticed, both on the Mackie CFX-20 and on the LX7, that the group-to-mix adds another layer of noise, so running input channels directly (which the Mackie can't do but fortunately the LX7 can) definitely cuts down on the noise a notch.

    I can also try a pair of auxes to see if the summing amps on those are any cleaner than the groups.

    But is there is anything else I can do, either with board configuration, or maybe even conditioning of the sound booth power circuits, that might help this? Or if the higher end boards will have lower noise floors due to better circuitry?

    Thanks. John
     
  5. DaveySimps

    DaveySimps CBMod CB Mods Premium Member

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    Typically higher end boards to have better circuitry, but there are always exceptions to the rule, of course.

    ~Dave
     
  6. avare

    avare Active Member

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    I do not understand this. Please explain. A1 controls house levels with master faders and input faders. Recording mix is off auxes, pre. Or are you sayng the A1 plays with pre gains?

    Andre
     
  7. SHARYNF

    SHARYNF Well-Known Member

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    If I remember correctly you are using Mackie srm 450's as your mains. These have an input that can work with line level all the way down to mic level. To keep the noise floor low, you need to get the levels up in the mixer so you are not running down in the "mud". Routing groups to mix on some mixers adds additional electronics into the path.

    A couple of things you could look at:

    Get a splitter on the outputs, and run your mix to cd record into a compressor
    When I have been doing a record of a simple number of outputs(vs a full split with dedicated mixer for recording) I use a whirlwind Matrix Mixer, it allows for 4 inputs to create any combination of 4 outputs or 4 direct thru's. This allows me to create a combined mix of the 4 outs.

    Look at ebay item 370003051861 as an example

    http://www.whirlwindusa.com/usaudio01.html scroll down to the mix 44

    As I mentioned above, get all your levels in the mixer UP and attenuate the inputs on the mackies to support it, so you are sending a higher level signal thru/out of the mixer

    Sharyn
     
    Last edited: Aug 4, 2008
  8. jkowtko

    jkowtko Active Member

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    Thanks for the info Sharon -- that Whirlwind mixer is interesting.

    Unfortunately the problem is not with the PA ... I agree that I should probably turn down the Mackies a bit (they're at 12 o'clock right now ... probably could be a little lower). But the PA is not the worst problem -- it's my recoding out of board.

    I actually am using two of the output busses through a compressor and into the recorder ... the compressor does a great job of curbing the peaks and preventing digital clipping (which sounds terrible).

    The noise I am finding is I think in the mix bus. If I push the mix fader up to zero I get a lot more noise than if I lower it down and raise the input channel fader levels. From adjusting the various "links in the chain" it seems like each mix bus adds a level of noise. So I can't just push the mix levels up, or else the noise will increase.

    I was hoping the move from a Mackie CFX to a Soundcraft board would result in lower noise floor ... looks like that's not completely true (ugh). If the theater had $8k to burn right now I'd probably call up FullCompass and order an LS9-32 and be done with this ...!

    By the way, I just bought parts to solder up my own splitters for the purpose you suggested -- in addition to providing a recording tap, it will also allow me to convert the L, R and M XLR output jacks into TRS so I can run all TRS cables from the mixer outs to the EQs.

    -- John
     
  9. jkowtko

    jkowtko Active Member

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    Fyi, for reference I've included URLs to two clips from different performances:

    (Group-To-Mix)

    http://insidesalesforce.com/Hillbarn/grouptomix.mp3

    (Mix-Only)

    http://insidesalesforce.com/Hillbarn/mixonly.mp3

    The "group to mix" clip was recorded with the input channels routing through Group 1/2, and then Group 1/2 routed to Mix. I recorded off of the Mix outputs. "Mix only" was with the input channels routing directly to Mix.

    I included the band playoff at the beginning so you could get a volume reference. In the Mix-only version I also pulled down the PA so the wireless faders were running hotter -- but in both tracks the band should be at roughly the same level, to the two tracks should be comparable recording volume.

    In the Mix-only version you will notice more reverb -- I had that turned up as well ... another difference that hopefully won't detract from hearing the noise floor on these clips.

    If you listen towards the end of the track after the ballgame on TV has been turned off, you'll hear the level of the noise floor and the difference between the two clips.

    So, the Mix-only clip has the noise floor to a tolerable level for me ... it isn't distracting when I turn up the volume to hear the dialogue more clearly. The noise floor on the "group to mix" clip IS distracting.

    I am curious as to your thoughts on these clips, and how this compares to recording you guys have done.

    Thanks. John
     
    Last edited: Aug 5, 2008
  10. FMEng

    FMEng Well-Known Member Fight Leukemia

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    The LX-7 is not a noisy board. I have used one many times for live music broadcasts. The source of the noise is improper gain structure, starting with the mic preamps and going through the whole console and on to the speakers. One clue would be that the console meters are barely registering when your music is fairly loud. A look at preamp levels with the PFL meter will also show them low.

    As Sharyn said, if you are driving SRM 450's chances are you have the mic preamps running too low because the speakers are too sensitive. Then, to get the level you need to the recorder you are making up the gain in later stages. That's a no-no. Always get the gain up to proper level right at the start of the signal chain.

    I would make some 10 to 20 dB balanced, resistor pads to put on the speaker inputs. That will get the console outputs up to average around +4 dBu, and peaks up around +18 dBu, where the console is designed to run.

    Also, your recording really needs its own mix. The dialog seems too low compared to the music. I would use post-fader aux busses to do a recording mix. That will allow you to change the proportions of various elements, but still follows your mix faders to keep operation simple on the fly.
     
    derekleffew likes this.
  11. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Amazing! Mixing tips and critiques right here on ControlBooth. If we all got webcams we could critique each other's lighting, live, also.:)

    Good advice, [user]FMEng[/user].
     
    Last edited: Aug 8, 2008
  12. jkowtko

    jkowtko Active Member

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    Thanks for the response.

    The input channel gain is already set pretty well. During mic checks I always level them between 0 and +10 on the solo meters.

    Right now the DBX231s are barely registering volume on the first LED of the 4-segment meter, which also confirms the low output of the board. I would assume that I should be operating around the 0 level on the EQ meters? Or do they like to run hotter?

    So it's probably just the input channel faders are being ridden too low, and maybe the mix buses as well. Yes, I can turn down the Mackies some, which in turn will ripple back through the chain and force the faders up more.

    Fyi, the reason I haven't done this before is because you can't notice any noise floor from the PA. I'm sure there is some, but the lighting and TD guys have built a pretty substantial noise floor into the theater, with dimmers mounted out in the open, no plexi around the follow spot, and some lights with motorized rolling gel changes that sound like a windup toy robot. (I don't think my kids could have done a better job at making noise ...!)

    Also, can I assume that the larger number of channels on the board contributes to higher noise floor through the mix bus? I was previously using a Mackie CFX-20, and I was able to mute only 5-6 channels on the LX7 for this production, so should I expect a noticable difference in the recording when summing 26 channels vs 20?

    But I will start by dropping the SRM450 gain from 12 o'clock to 11 or 10, and see how it affects the rest.

    Yes, it would be nice to run a second board or 24 track recorder, using pre-fade direct outs, and mix separately for the recording. But that's not really feasible right now (space and equipment) so I'd rather tackle the issues that are within reach first.

    But thank you for the feedback :)
     
    Last edited: Aug 8, 2008
  13. jkowtko

    jkowtko Active Member

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    One other thing -- and this was my bad for not realizing this "bonehead" move sooner -- I had the recorder plugged into a different circuit than the sound system. It's a digital recorder, but connected via analog cable to the sound system. More noise here? (I did not get any Ground loop hum).

    Fyi, I also had compressors plugged into all 12 vocal input channels. Unbalanced insert cables -- not sure if that contributed to the noise as well.

    So, lots to investigate here ;)
     

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