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EQ modules clip way too easily
by chimp_spanner on 2012-11-15 03:14:53

Hey all. Firstly just want to say that overall, I'm very pleased with the HD now especially after the latest update. I still feel that it's severely lacking in the EQ department, although I don't want to get into feature requests. One thing I've noticed, though, is that the EQ we do have clips so easily. I have to halve my channel volume in order to avoid it, which means boosting the input on my interface and raising the noise level at the same time. It's not even just in a post amp situation either. Using EQ before the amp block, with everything turned off, there's still clipping just from the dry signal unless I waste an FX block with a volume pedal before the EQ. And yes, I've tried padding. Even if that did work, it shouldn't be necessary given that a clean tone with no FX does not overdrive either the POD or my audio interface.

Any thoughts on this? Anyone else experiencing the same thing?



Re: EQ modules clip way too easily
by MartinDorr on 2012-11-15 10:00:57

I am in the process of measuring the Studio EQ's gain transfer function because I noticed the same thing. From what I found out so far is that the Studio EQ does not seem to just apply the dialed in gain but also compresses and distorts the signal in a gradually increasing fashion when its output level exceeds about -3dB. I am not excatly sure what's going on but it sounds as if it clips way below 0dB. I am measuring via USB so I can't tell whether the HD internal signal level between effect blocks is higher than what is produced on its USB output. If there are differences between effect paths it is not so for all functions because the mixer seems to be fine adjusting gain up to 0dB output w/o clipping or distortion.

Watch out with the Studio EQ gain dial. The output gain may be up to -2dB off from what you dialed in. It seems the dial is only correct at 0dB and at the very ends of +/-18dB (and only if its output is less than about -3dB). I am in the process of compiling a lookup table showing what to set to get a specific gain. I have 1 set of numbers but I need to check it for different input levels as I suspect the deviations are due to rounding errors, i.e., you may get different dial discrepancies based on what your input level is.

Another thing I noticed is that different EQ's have different default gain values at their default setting. Only about half do not change the tone in their default setting. I have a list at home and will post later tonite.

Hope this helps you in some way,

Martin



Re: EQ modules clip way too easily
by DeanDinosaur on 2012-11-15 12:57:37

As much as I dislike the EQ in the POD, I still use it and have no problems clipping. I'm mot sure what you mean by clipping. I'm placing the EQ (focus) infront of whatever amp and cranking it to max to drive the amp. It's very effective and the only clipping I'm getting is desirable clipping. the only undesirable clipping I'm aware of is if you place an EQ, modulation or any effect after the Mixer and push the mixer above zero, some effects can be clipped undesirably. As long as your mixer levels are at zero, it's all good from my experience even though I have a few patches with the mixer above zero..



Re: EQ modules clip way too easily
by chimp_spanner on 2012-11-15 13:13:53

I've actually been putting the EQ's after the mixer block - moved them in front of it and 100% improvement - no clipping. Very helpful, thank you! I have still experienced clipping within the EQ when used in a pre amp position, and I still don't like that some of them colour the sound in their default/neutral setting. But still, this is a great help to me.



Re: EQ modules clip way too easily
by MartinDorr on 2012-11-15 13:30:47

I was mostly reporting about my experience with the Studio EQ. The Mid Focus EQ could be quite different in regard to how it responds to gain changes. Unless I remeber wrong, the Mid Focus EQ changes the tone even at its default setting. I am not sure it even has a neutral setting. Although a neutral starting point might be nice it is probably not a big issue as one obviously wants the Mids focussed when it's selected ;-). Will play tonight and see what it does with just dialing in gain.



Re: EQ modules clip way too easily
by MartinDorr on 2012-11-15 13:39:12

If your mixer was set to position both channel A and B hard center in a single Amp tone you added 6dB to your Amp output signal before it was EQ-ed. Moving your EQ to pre-mixer you may have reduced the EQ input by 6dB. This may not apply if channels A and B were panned hard left and right at 0dB. Just a thought.

Martin



Re: EQ modules clip way too easily
by scottyo78 on 2012-11-15 16:05:21

Maybe you've seen it... if not, check this youtube video out about the HD's EQ's.

It's pretty informative... and I laugh when he talks about correlating Line 6's silly use of percent (%) for many of the values on what... 3 of the 5 available EQ's.

I've also read MeAmBobbo's Guide on EQ. Personally, I don't have the patience to use them, don't notice that much difference when I have and typically get a tone I'm happy with just using the Amp Settings.



Re: EQ modules clip way too easily
by chimp_spanner on 2012-11-15 16:31:43

Pffff, man, I gotta say that while that's a really useful video (and I'll be writing down some of those values for future use) it should really illustrate just how badly thought out the EQ section is on the HD. It's pretty crazy, considering everything else is reasonably well thought out. I would be quite happy if they completely scrapped the existing models and just gave us one effect with a HP, LP and one, maybe two parametric bands, in hz and dB. I'll gladly take that over "shift" and "mid focus", and I'd be willing to be you could achieve all the same sounds. I hope more than anything that this is addressed in the next firmware. Of course for recording purposes I can always just EQ in my DAW, but I like to get the tone as close to what I want at source. Anyway thanks for the links and info guys.



Re: EQ modules clip way too easily
by DeanDinosaur on 2012-11-15 16:48:09

chimp_spanner wrote:

... I would be quite happy if they completely scrapped the existing models and just gave us one effect with a HP, LP and one, maybe two parametric bands, in hz and dB. I'll gladly take that over "shift" and "mid focus",...

I can't think of anyone who uses EQ who wouldn't like that. I still don't understand why this hasn't been a priority...



Re: EQ modules clip way too easily
by meambobbo on 2012-11-15 18:31:33

yes - mid-focus is the worst offender, followed by the parametric and graphic.  don't use the shift, so I can't speak on that.  The Studio EQ is actually the best as far as not clipping IMO.  i don't use it that often, but never noticed any compression; however, i was never listening for it.  i'm curious to know about this...

one explanation is that line 6 is accurately modeling the EQ's the effects are based on.  I can't comment on that since i've never used the real-life counterparts, but I have trouble believing any real-life EQ could clip when being connected directly to a guitar.  I also have to doubt they'd have an output parameter that couldn't be driven to 100% without clipping.

in addition to input clipping, i've found the Studio and Mid-Focus can clip if you boost their Gain parameter too high, regardless of other settings and even the input signal level.  I never boost past 65% on the mid-focus and the highest i'll go on the studio is about +12 db.

the mid-focus is far from neutral at default but can be made so.  HP freq 0%, HP Q 55%, LP 100%, LP 55%, Gain 0%.

the mid focus is a great set of HP and LP filters, other than the clipping issue.  if combined with two parametric EQ's, you have a pretty comprehensive EQ.  What I would like is a dual parametric EQ that does not have the Lows/Highs parameters.  If you notice, most effects have no more than 6 parameters.  2 for HP, 2 for LP, 3 per parametric band x2 = 10 parameters.  I wouldn't expect that anytime soon.  But dual parametric would be 6, so use that plus a mid-focus.  It'd be 2 blocks rather than 1, but that's not much difference.

anyway, considering we can't even get frequency in HZ, I'm going to go ahead and say that after 2 years without so much as an official acknowledgement of the many flaws of the EQ's, Line 6's treatment of this issue is a complete joke and has seriously given me doubts about whether I will ever buy another Line 6 product.  DON'T GET YOUR HOPES UP THIS WILL EVER BE IMPROVED.



Re: EQ modules clip way too easily
by MartinDorr on 2012-11-15 21:25:20

OK, I did a little more checking. I used a Variax with Volume and Tone @ 100%, Strat Neck position as source. Input 1 is Variax and input 2 is set to Guitar (the equivalent of None) which gets me -105dB noise level when not playing. My mixer is set at 0dB with channel A and B hard left and right, respectively. If I record 1 hard strumm with the looper in pre position I get a very clean output signal at -16.4dB measured on a DAW via USB. This is my reference tone for all the following:

Adding the following EQs with default settings in pre-mixer position I get the following output level changes:

  • Graphic EQ:        + 2.9dB (doesn't have a tone neutral gain knob)
  • Parametric EQ:    - 0.1dB (has neutral gain knob with % dial, 0% = -15.8dB, 100% = +7dB for a -16.4 dB input)
  • Studio EQ:          - 0.1dB (has neutral gain knob with dB dial, -18dB = -34.4dB, (compresses and sounds clipping on high dB gain end)
  • 4 Band Shift EQ: - 0.1dB (doesn't have a neutral gain knob)
  • Mid Focus EQ:    +8.2dB (change tone at any gain setting, % dial, 0% = -19.6dB, 100% = -2.4dB (compresses and sounds clipping at high % end)

Checked a little more into Mid Focus EQ % to dB output transfer function. There are clear indications that the EQ starts compressing and later on distorting (not sure about clipping as it never hits 0dB) at around -12dB! output level. As long the output stays below -12dB you get about 2.4 dB gain for every 10% increase on the gain knob.

I suspect that Line 6 models the real HW with an assumed headroom ending at 0dBFS (digital maximum). Given that most historic profesional audio equipment provided 10-16dB headroom I suspect any input level above this professional headroom (different for different EQs) will first run into anlalog equipment like soft compression and finally distortion and very little if any clipping due to the modelled behavior. Obviously this is a lot of guessing but look at a few samples numbers yourself:

   %    -16.4   -26.4   -25.7   Input Levels in dB

    0    -19.6   -29.6   -28.9   Output levels in dB with % gain from left

  10    -17.2   -27.2   -26.5

  20    -14.8   -24.7   -24.0

  30    -12.4   -22.4   -21.7

  40    -10.1   -19.9   -19.3

  50    -08.2   -17.6   -16.9

  60    -06.6   -15.2   -14.5

  70    -05.3   -12.7   -12.1

  80    -04.1   -10.5   -09.9

  90    -03.1   -08.5   -08.0

100    -02.4   -06.8   -06.4

One can see that for all output levels less than -12dB the difference between a 10% gain knob change is 2.3, 2.4, or 2.5 dB (twice my meter resolution, i.e., my maximum error) while all output levels higher than -12dB get more and more compressed as the output level approaches 0dBFS. I have gone back checking but I suspect the Mid Focus EQ can do a clean 24dB gain range with its 0% to 100% gain knob setting as long as its output level does not exceed -12dB.

The other EQs and possibly other effects are likely similar with their own 'headroom' characteristic. I have evidence that the Studio EQ's compression seems to start around -10dB and gets really distorted starting around -3dB.

So for me it looks like the input levels to EQ effects and output gain dials need to carefully set to only get the 'EQ' effect you may want. But I'd guess a little soft analog-like compression/distortion does not hurt either when its wanted and can be had essentially for free in the EQ you need anyway if the gain is carefully placed ;-).

... and it looks like what I found is right in line with you guys experience. Hopefully just a little more background why it happens and some tools to avoid it.



Re: EQ modules clip way too easily
by MartinDorr on 2012-11-15 21:28:00

Forgot to mention that my Amp is disabled, i.e., I have the looper as a reference source with known output, the EQ, the mixer and measure USB out.



Re: EQ modules clip way too easily
by CairnsFella on 2012-12-05 21:44:31

Interesting read. Thanks guys.

Still, at the rate I am getting around to try out various elements of my HD, I'm hoping (albeit with optimism to the max) that the EQ is resolved before the current set up bugs me too much.



Re: EQ modules clip way too easily
by meambobbo on 2012-12-07 20:33:53

Excellent research, but I disagree with this statement about the mid-focus eq ("change tone at any gain setting").  With the default LP/HP settings, yes, the tone is clearly different, but putting HP freq at 0% and LP freq at 100% and moving the Q's up to 55%.  You also have to keep the output levels relatively low as you mention to prevent clipping/compression.



Re: EQ modules clip way too easily
by scottyo78 on 2012-12-08 19:17:38

Thanks guys for all the research and input for the EQ's.

My gosh, it sounds (literally, pun intended ) like Line 6 really screwed the pooch on all their EQ's. I also have noticed they distort  and they don't boost where expected, so as I've said in other posts, I don't use them. To get even a decent sounding response they require way too much futzing. To me they are just a "Black Box" mystery effect and using them gives unexpected results.

I get by with the Amp's EQ and using some of the tone shaping on the distortions, overdrives and the Boost compressor.



Re: EQ modules clip way too easily
by MartinDorr on 2012-12-10 08:06:22

Yes, you are right. I missed your earlier comment on a non-default setting that makes the Mid Focus EQ tone neutral. I have since gone back and checked and I think you are right on with your sugested setting. I have a little cheat sheet of the measurements and conclusions about the Mid Focus EQ written in Word. I am in the process of collecting similar material for the Studio EQ and Amps. Any opinions on how to best post it? And congrats to your son ... looking good ... enjoy!

Martin




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