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1418 Views 21 Replies Latest reply: Apr 5, 2012 11:08 AM by meambobbo RSS
mdmayfield Just Startin'
mdmayfield
353 posts since
Feb 24, 2007
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Apr 3, 2012 10:42 PM

Analyzing what the new Cab Deep Edit Parameters do

I had a brief moment tonight to do some frequency analysis of the new parameters - the thing I was most excited about, since the Low Cut will make the Marshall cabs actually usable without drowning out my bass player in thundering mud.

 

For the EQ curve analysis, I just used the hum from a guitar cable going to nowhere. It is pretty useful for seeing what is happening with the low cut filter.

 

Here's the link. I'll try to do some more this week with real test signals, too.

 

http://youtu.be/53MtkBSRXT0

 

Matt

  • maqaf1 Just Startin'
    maqaf1
    73 posts since
    Mar 25, 2007
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    Apr 4, 2012 12:02 AM (in response to mdmayfield)
    Re: Analyzing what the new Cab Deep Edit Parameters do

    Thanks, Matt

  • mazuwa Iknowathingortwo
    mazuwa
    371 posts since
    Jul 7, 2006
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    Apr 4, 2012 1:22 AM (in response to mdmayfield)
    Re: Analyzing what the new Cab Deep Edit Parameters do

    The manuals have not been updated. Hopefully they will say a view words later.

  • meambobbo Iknowathingortwo
    meambobbo
    1,702 posts since
    Dec 13, 2007
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    Apr 4, 2012 8:37 AM (in response to mdmayfield)
    Re: Analyzing what the new Cab Deep Edit Parameters do

    well here's an interesting question - do the DEP's do the same thing on every cab, or do different cabs respond differently to these DEP's?  For example, resonance seemed to increase 2 spots in the spectrum more than others - one about 600 HZ and the other around 1800 HZ.  Maybe these spots are different or wider for different cabs?

     

    Also, I'm not sure that thump is simply a boost/cut - the documentation says it reacts with the resonance.  So I think it's got more of a boomy kind of tone like when you use a lot of bass in your tone and really push a real cab.

     

    i think resonance is the same way - it's forcing tones towards certain frequencies since the cab has certain resonant frequencies.

     

    I think you'd hear it better on a variety of guitar playing - a single pitch hum is good for analysis like you did but it's not going to tell the whole story of how it will affect guitar tone.

    • mdmayfield Just Startin'
      mdmayfield
      353 posts since
      Feb 24, 2007
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      Apr 4, 2012 9:15 AM (in response to meambobbo)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      That's a good question and I plan to take a look at that.

       

      I suspect that the cab models are effectively something like impulse responses, but not just static "click" recordings like traditional IRs. I think they might be dynamic, as in they would respond nonlinearly in order to emulate speaker breakup. That might mean that the HD is constantly live-rendering the cab's impulse response in realtime. If that's so, then those parameters are influencing the way it renders the cab's response.

       

      Here's my first guess at what's going on with these parameters, to be corrected & refined by further study, based on what I saw last night.

       

      Low Cut - probably a straightforward 12dB/octave high pass filter, but applied to the cabinet "live IR" rather than the post-cab signal. (The result is similar, but not identical.) I'm also going to guess that this one doesn't change depending on the cab.

       

      Resonance - I suspect this one changes depending on the cab. My current guess is that it determines how strongly the cab's character is applied to the sound (i.e. exaggerating or smoothing the cabinet's frequency response).

       

      Thump - possibly a straightforward low shelving filter, again applied to the cabinet's response.

       

      Decay - Not exactly sure yet, but it seems to affect the cabinet's response over time. I heard greater resonance and ringing with it set lower than when set higher. I think a waterfall plot will help get to the bottom of this one.

       

       

      As far as hearing it on playing instead of test signals, yes, obviously the end goal is to use it for guitar sounds. But some of the effects of the parameters are subtle enough that it's hard to deduce exactly what's going on just from the sound with a guitar. For example, increasing Resonance or decreasing Decay have similar, but not identical effects. I want to know objectively / theoretically what's happening to the sound, in order to make better informed decisions about practical tone tweaks.

    • jimsreynolds Power User
      jimsreynolds
      2,227 posts since
      Jun 27, 43450
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      Apr 4, 2012 11:22 PM (in response to meambobbo)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      As I understand Resonance in the real world:  it is a control that effects the amount of negative feedback within the power amp.  Negative feedback is signal from the output stage, fed back into the signal chain, used to make an amp more linear and clean in terms of dynamics and frequency response.  Higher feedback = flatter response.  

       

      Marshall plexis have high negative feedback and need to be cranked before the power amp stage starts to break up.  Vox AC30's have no negative feedback (IIRC) and are very dynamic indeed.

       

      Resonance affects low frequency negative feedback.  With the resonance turned up, less Low end negative feedback is passed through.  This makes the low end more dynamic and growly.  Presence does the same thing at the high frequencies.


      I think that you may need to see changes in amplitude before the effect of Negative Feedback shows up on a plot.

       

      Interestingly, all of this has nothing to do with actual speakers and everything to do with the power amp but hey, who cares.

       

      Ready to be slapped down by the higher level techs here ...

      • meambobbo Iknowathingortwo
        meambobbo
        1,702 posts since
        Dec 13, 2007
        Currently Being Moderated
        Apr 5, 2012 6:58 AM (in response to jimsreynolds)
        Re: Analyzing what the new Cab Deep Edit Parameters do

        hey jim - since the amp blocks and cab stuff are married together, maybe you're right that this is power amp negative feedback; however, resonance is also something that occurs in cabinets (especially closed back) when you push them.  The size, shape, materials, and construction of a cabinet will affect resonant frequencies and provide positive or negative interference with the current signal the speaker is trying to express.  Given that the new parameters are referred to as cab DEP's, I would think this is what is attempting to be modeled; however, the general effect is likely similar to negative feedback in a power amp.

  • alfmetal70 Just Startin'
    alfmetal70
    104 posts since
    Feb 3, 43473
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    Apr 4, 2012 4:18 PM (in response to mdmayfield)
    Re: Analyzing what the new Cab Deep Edit Parameters do

    thanks, very good job, greetings!

  • mdmayfield Just Startin'
    mdmayfield
    353 posts since
    Feb 24, 2007
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    Apr 5, 2012 7:54 AM (in response to mdmayfield)
    Re: Analyzing what the new Cab Deep Edit Parameters do

    Well here's what I found by doing Impulse Response measurements and waterfall plots.

     

    http://youtu.be/0SXWIXHBpWY

     

    I don't have the expertise & tools to go very much further in the analysis, but it shows that my first guess above was mostly wrong. In fact, Delay looks like it has the opposite effect that I thought I saw before (though this might be related to a different cab model).

     

    To try to be more helpful/useful, I am just finishing up another video that shows what frequencies those stupid % numbers are on the EQ effects.

     

    Matt

     

     

    EDIT: whoops, I see that forum member meambobbo has already done an EQ test on the Parametric EQ: http://line6.com/support/message/235242#235242   But, if you would like to see it, the video I made is here and covers all the EQs that use percentages: http://youtu.be/wLkVhOp5FCY

     

    Message was edited by: Matt Mayfield

    • meambobbo Iknowathingortwo
      meambobbo
      1,702 posts since
      Dec 13, 2007
      Currently Being Moderated
      Apr 5, 2012 7:58 AM (in response to mdmayfield)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      matt, the more tests we have on the %'s the better - my test may have been slightly off or my frequency analyzer could be...  so far we only have 2 and that's just for the PEQ.

       

      i'll try to analyze the video and document your findings in my guide:

      http://www.foobazaar.com/podhd/toneGuide

    • meambobbo Iknowathingortwo
      meambobbo
      1,702 posts since
      Dec 13, 2007
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      Apr 5, 2012 7:59 AM (in response to mdmayfield)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      what spectrum analyzer are you using?

    • meambobbo Iknowathingortwo
      meambobbo
      1,702 posts since
      Dec 13, 2007
      Currently Being Moderated
      Apr 5, 2012 8:38 AM (in response to mdmayfield)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      hey i'm digesting the video right now.  GREAT WORK!  I'm typing up my own analysis.  The only real difference I'm finding from what you are saying in the video is that I believe you are reading the frequency chart linearly rather than exponentially.  IE if you see a peak directly between the 50 and 100 HZ lines, you might say it's 75 HZ, but it's actually more like 65-70 HZ because of the exponential scale.

      • mdmayfield Just Startin'
        mdmayfield
        353 posts since
        Feb 24, 2007
        Currently Being Moderated
        Apr 5, 2012 9:20 AM (in response to meambobbo)
        Re: Analyzing what the new Cab Deep Edit Parameters do

        Thanks! That looks great! True, I was a bit sloppy at estimating the frequencies. The analyzer is the one built into Logic's Channel EQ; I suppose I could have put lined up of the filters with the peak in the noise and read the number off.

         

        Re: the waterfall graphs, yes, that is what I see as well, but it's not clear exactly how it's working behind the scenes. Any ideas?

        • meambobbo Iknowathingortwo
          meambobbo
          1,702 posts since
          Dec 13, 2007
          Currently Being Moderated
          Apr 5, 2012 11:08 AM (in response to mdmayfield)
          Re: Analyzing what the new Cab Deep Edit Parameters do

          my theory is that they simply apply reverb to the IR signal, maybe with a slight pre-delay as well as EQ it to filter out anything that's not supposed to resonate.  it definitely looks like a comb filter, which should look more and more jagged as the frequencies get higher and higher, and that's what i'm seeing in your waterfall graphs.  the same signal with a slight delay would produce such comb filtering.  as for thump, i'm betting its just a bass boost applied to the EQ filter on the resonance reverb.  as for decay, I would think this is just the reverb's decay setting.  there could be a lot more to this, but i'm going to go with occam's razor.

    • meambobbo Iknowathingortwo
      meambobbo
      1,702 posts since
      Dec 13, 2007
      Currently Being Moderated
      Apr 5, 2012 8:52 AM (in response to mdmayfield)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      ok - here's my analysis:

       

      Parametric EQ

       

      This EQ features one fully parametric band (freq, Q, gain) and two shelves (lows, highs).

       

      Low shelf - around +/-15 db of gain, with everything below 100 HZ flat and a slope from 100 HZ to 200 HZ.

      High shelf - around +/-12 db of gain, with everything above 2 kHZ flat and a slope from 1 kHZ to 2 kHZ.

      Paremetric Band - around +12/-15db of gain, Q ranges from around 8 octaves to 1 octave going from min to max settings.

       

      0   -   50 HZ

      10  -  100 HZ

      20  -  180 HZ

      30  -  300 HZ

      40  -  525 HZ

      50  -  850 HZ

      60  - 1350 HZ

      70  - 2000 HZ

      80  - 2600 HZ

      90  - 3600 HZ

      100 - 4700 HZ

       

       

      4 band shift EQ

       

      this provides 4 peak/dip band EQ's with gain denoted in db's already.

       

      Lo freq - centered around 90 HZ with shift at 50%, about 2 octaves wide

      Low mid - centered around 180 HZ with shift at 50%, about 2 octaves wide

      Hi mid - centered around 1 kHZ with shift at 50%, about 6 octaves wide

      High - centered around 4 kHZ with shift at 50%, about 5 octaves wide

      Shift - causes the low and low mids bands to shift from higher to lower center frequencies, while causing the high and high mids bands to shift from lower to higher center frequencies, as shift moves from 0 to 100%.  Shift move the center frequency of each band about 1 octave from its min to max setting.

       

       

      Mid Focus

       

      as the name implies this boosts the mid frequencies by means of a high pass and a low pass filter.

       

      its default settings are for a heavy mid boost.  To make the EQ neutral, set hp freq 0%, lp freq 100%, and turn gain down to almost 0%.

       

      The Q settings affect the slope the rolloff, and at 100%, they actually form a resonance peak that actually slightly boosts the signal before rolling off above or below that point.  below are the frequencies of these resonant peaks at 100% Q.

       

      high pass

      0   -    0 HZ

      10  -   65 HZ

      20  -  110 HZ

      30  -  160 HZ

      40  -  205 HZ

      50  -  250 HZ

      60  -  325 HZ

      70  -  400 HZ

      80  -  450 HZ

      90  -  500 HZ

      100 -  525 HZ

       

      low pass

      0   - 500  HZ

      10  - 600  HZ

      20  - 800  HZ

      30  - 1.2 kHZ

      40  - 1.5 kHZ

      50  -   2 kHZ

      60  - 3.5 kHZ

      70  -   6 kHZ

      80  - 8.5 kHZ

      90  -  12 kHZ

      100 -  18 kHZ

    • meambobbo Iknowathingortwo
      meambobbo
      1,702 posts since
      Dec 13, 2007
      Currently Being Moderated
      Apr 5, 2012 9:08 AM (in response to mdmayfield)
      Re: Analyzing what the new Cab Deep Edit Parameters do

      also, from the waterfall graphs, looks like the cab DEP's tend to introduce more resonant peaks and comb filtering, yes?

  • KozMcCharlie Just Startin'
    KozMcCharlie
    179 posts since
    Oct 5, 2008
    Currently Being Moderated
    Apr 5, 2012 10:41 AM (in response to mdmayfield)
    Re: Analyzing what the new Cab Deep Edit Parameters do

    Not sure if it helps, but it seems that pink noise would be a more consistant way to go.

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