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Compressor Distortion
Old 29th June 2010
  #1
Gear Maniac
 

Compressor Distortion

I did a search on this subject and found it not uncommon for some compressors to crackle when using fast attack and release combinations on guitars. I've been recording a Strat run through a Mesa Boogie getting that real "thwank!" sound. I wanted to use a compressor to level out some of the more aggressive moments in the performance. Two compressors I tried, the 1176 spin-off in a 6176 and an MC77 both would crackle/distort on these hard hammered transient notes. There was definitely a relationship between faster attack and release settings. The faster settings yielded the most distortion while backing off tamed the crackling somewhat. I even tried bypassing the compressors, recorded the signal straight and tried the UAD 1176 emulation and it caused the same distortion.

There must be some issue with the way these very fast attack/release compressors grab that causes this crackling at the peak of these hard signals coming from the Strat. I tried different mics, different pre-amps, different pre-amp settings, and still the distortion was there. I use both these compressors for vocals also and have never encountered any issues like this.

I tried my OCL-2 with a Fast setting and a fairly high ratio with the same signal and the crackling was not there. I know the OCL-2 has a softer knee and therefore somewhat gentler grabbing characteristics. Whatever it is, unlike the 1176 and the MC77, I had no issues with it.

I'm just rather curious from a theoretical standpoint of why these particular compressors, and indeed even the emulation of one, crackle and distort when an aggressive guitar signal of this nature is passed through them.

Any ideas?

Regards,

DB
Old 29th June 2010
  #2
Gear Head
 
Izhaki's Avatar
 

Hi DB,

There are two reasons for this and these are linked to some extent:
  • Compressors are non-liner devices and as such they generate distortion by the very nature of their operation. With light compression, this distortion is hardly audible. But with hard compression, you start hearing distortion. 'Hard compression' means fast changes in gain reduction. Fast attack and release times mean faster changes in gain reduction - making the compressor a (far) less linear device, and thus you get more distortion.
  • As low-frequencies have longer periods (the waveform develops slower over time in comparison to high frequencies) a compressor can actually act within the cycle of a low frequency provided the attack/release are short enough. This reshapes the waveform quite drastically and in turn generates a very audible distortion. You can see this happening in the attached screenshot (top is before compression, bottom is after).

The 1176 is 'wild' by design - it's circuitry is rather 'dirty' due to the somewhat-not-as-solid technology that was about in the days it was designed, it offers very fast attack and release times, with an option to bypass the attack stage (making it more of a waveshaper); the internal curves for the attack and release stages are ones resulting in a more 'obvious' compression. All contribute to overall a very non-linear, like-to-distort type of box.

The OCL-2 is electro-optical, and as such you should expect its fast attack to be much slower than that of the UREI or many other compressors.

Hope this helps.
Attached Thumbnails
Compressor Distortion-pt-lf-distortion.jpg  
Old 29th June 2010
  #3
Gear Maniac
 

Thanks Roey...and yes, that helps very much.

I've noticed before that bass frequencies have little issue with unpleasant distortion in the 1176 and MC77. The issue seems quite apparent though with higher frequency content on a hot transient signal (like the signal from a guitar). In the session yesterday the guitar signal had a significant boost in the 4-6k range to emphasize that Strat "bite"...as the Mesa Boogies get a little bass heavy when overdriven. Again that explains why vocals have little issue with unpleasant distortion in these units as they are not really hot signals, per se, that might drive hard to compress upper frequencies.

Thanks again for taking the time to enlighten me. Much appreciated.

Regards,

DB
Old 30th June 2010
  #4
Gear Maniac
 

Quote:
Originally Posted by dbowman View Post
Thanks Roey...and yes, that helps very much.

I've noticed before that bass frequencies have little issue with unpleasant distortion in the 1176 and MC77. The issue seems quite apparent though with higher frequency content on a hot transient signal (like the signal from a guitar).
Interesting. Low frequencies are more prone to distortion for fast settings, as explained in Izhaki's post.

Are you sure what you're hearing is distortion from the compressor and not just more of the guitar tone being more audible after the compression?
Old 30th June 2010
  #5
Lives for gear
 
grrrayson's Avatar
 

It sounds like you're describing exactly what an 1176 will do with a transient source with a fast attack setting. I don't think anything is necessarily wrong here.

Did you try different ratios and gain structures, though?
Old 30th June 2010
  #6
Lives for gear
 

Quote:
Originally Posted by dbowman View Post
I wanted to use a compressor to level out some of the more aggressive moments in the performance.
I know it's tempting to use a comp for this, but wouldn't a fader movement or automation be a classier approach?
Old 26th April 2014
  #7
Gear Maniac
 

With FET and 1176 style compressors, if you use fast release with distorted guitars, you get an awful distortion during the release.
That is done too with the limiter of the apogee converters. In the mini me was terrible.
Old 1st August 2014
  #8
Gear Head
 

Well, the plus side is this thread saved me from taking an 1176 into service. The downside is the 1176 distorts too much for me to squash this guitar sound i got over here. Too bad, the all buttons in with fast attack on a guitar "room" mic sounded great otherwise.
Old 1st August 2014
  #9
Mho
Lives for gear
 

Use automation or clip gain to control crazy dinamic range and opto style compression to smooth the transients a little.
Old 1st August 2014
  #10
Gear Guru
 
Brent Hahn's Avatar
 

Quote:
Originally Posted by Slack View Post
Well, the plus side is this thread saved me from taking an 1176 into service. The downside is the 1176 distorts too much for me to squash this guitar sound i got over here. Too bad, the all buttons in with fast attack on a guitar "room" mic sounded great otherwise.
A variable knee mod for the 1176 would be a nice thing.
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