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Post by geoff738 on Jun 22, 2016 21:23:07 GMT -6
I perhaps should have prefaced this as perhaps a dumb question about PWM Compression. But here goes.
When I was a young pup trying to learn about compression, the mags would talk about the various compressor topologies, and they'd list Vca, Fet, opto, and vari-mu. And invariably there would be an example mentioned for each type. Depending on when we're talking, you were likely to see Dbx (and others), 1176, La2a, and Manley or Fairchild respectively, as representative of that particular compressor type. Often along with descriptors like fast, grabby, smooth, etc. Of perhaps dubious utility.
But I don't recall seeing PWM, or diode bridge for that matter discussed.
So, are these actually different compressor types, or do they fit in with the above categories? And what would be examples of PWM and diode bridging?
The Great River is a PWM I think, but I've never used one.
Was the ADR Compex a diode bridging?
Thanks in in advance for enlightening me and hopefully others.
Cheers,
Geoff
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Post by jin167 on Jun 22, 2016 21:31:27 GMT -6
Pye, crane song, dw fearn, great river to name a few.
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Post by geoff738 on Jun 22, 2016 21:47:42 GMT -6
Pye, crane song, dw fearn, great river to name a few. Yeah, but I hear they all suck.  Trakker is PWM? I'm familiar with that, but it's doing a Swiss Army knife thing. Which I'm guessing the Pye might not be. Cheers, Geoff |
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Post by ChaseUTB on Jun 22, 2016 22:21:19 GMT -6
Pye, crane song, dw fearn, great river to name a few. Yeah, but I hear they all suck. Trakker is PWM? I'm familiar with that, but it's doing a Swiss Army knife thing. Which I'm guessing the Pye might not be. Cheers, Geoff Neve 2254 and 33609 are diode bridged compressors A note from Geoff Tanner regarding Neve Compressors "Neve limiter compressors have two side chains... The limiter side chain hangs on the unbalanced output of the module to catch everything above the threshold. It just takes the signal, runs it through a stepped attenuator, a buffer amp, rectifier, time constant (attack and recovery) and then sends the dc (mixed with any compress sidechain dc) to the diode bridge. The compress side chain is much the same except that it has a law shaping section and hangs on the input side of the module. The diode bridge sits between two transformers and is fed from a balanced attenuator of about 40dB. When the diodes are non-conducting, -40dB passes over them. As the bias voltage increases the diodes pinch the two balanced limbs progressively together. A neat and very simple system with one drawback.... on the 2254 the gain make up is actually a 20dB attenuator that you progressively release as you rotate the gain make up knob. This means that, even when it's not doing anything, you are throwing away 40dB in the diode attenuator and a further 20dB in the gain make up control. The 2254 uses a BA283AV (as in a 1272) to make up the 60dB loss back to unity gain. Making up that loss brings up the noise floor. All the later Neve compressors use a 440 or 640 amplifier and, rather than reducing an attenuator, the 20dB gain make up is made up by gain boosting the 440/640 which is the only amplifier in the audio path. As the maximum gain of a 440 is supposed to be 40dB, I often wonder what the figures on THD are with the extra 20dB added... though, to be fair, I don't think many folk crank the gain up that much." |
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Post by jin167 on Jun 22, 2016 22:35:14 GMT -6
Pye, crane song, dw fearn, great river to name a few. Yeah, but I hear they all suck. Trakker is PWM? I'm familiar with that, but it's doing a Swiss Army knife thing. Which I'm guessing the Pye might not be. Cheers, Geoff yeah they all sound pretty horrible  not sure about the trakker I was referring to their stc-8. |
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Post by EmRR on Jun 23, 2016 6:56:45 GMT -6
Diode bridge types go back to the 1930's, but never the most common type.
There's a Grass Valley PWM comp from 1960 I've wondered if might be the first.
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Post by Ward on Jun 23, 2016 10:55:31 GMT -6
Sometimes the reason a design is not that discussed is because it sucked, not because someone was trying to keep anything from the audio engineering world (esp Newbies).
It's like the solid state preamp, tube driven power amp guitar amplifiers.. like Peavey and Music man.
Most of us hate them
A few people like them.
People who have no taste.
LOL
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Post by svart on Jun 23, 2016 11:05:55 GMT -6
I love my 2254. You can't set too much ratio or the compression sounds funky, but for anything up to around 4:1 it's incredibly fast. The sidechains are separate, and you're able to shut one or both down. The compression is rather round sounding, like it follows the envelope of the signal rather than simply reducing gain. It's hard to explain but it's definitely a distinct sound.
I'm thinking about another one now.
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Post by mdmitch2 on Jun 23, 2016 11:08:18 GMT -6
I love my 2254. You can't set too much ratio or the compression sounds funky, but for anything up to around 4:1 it's incredibly fast. The sidechains are separate, and you're able to shut one or both down. The compression is rather round sounding, like it follows the envelope of the signal rather than simply reducing gain. It's hard to explain but it's definitely a distinct sound. I'm thinking about another one now. Is that the AML version or something else?? |
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Post by svart on Jun 23, 2016 11:11:14 GMT -6
I love my 2254. You can't set too much ratio or the compression sounds funky, but for anything up to around 4:1 it's incredibly fast. The sidechains are separate, and you're able to shut one or both down. The compression is rather round sounding, like it follows the envelope of the signal rather than simply reducing gain. It's hard to explain but it's definitely a distinct sound. I'm thinking about another one now. Is that the AML version or something else?? Nah it was my own build. realgearonline.com/thread/1393/2254-33609-build-finished-calibration |
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Post by dandeurloo on Jun 24, 2016 16:28:37 GMT -6
I've not heard a pwm compressor I don't like (I like my mxr 136 after my mood).
I didn't know DW Fearn made one. Is that true?
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ericn
Temp
Balance Engineer
Posts: 15,011 
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Post by ericn on Jun 24, 2016 16:36:43 GMT -6
I've not heard a pwm compressor I don't like (I like my mxr 136 after my mood). I didn't know DW Fearn made one. Is that true? Come on Dan we need a ZOD Comp! |
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Post by chasmanian on Jun 24, 2016 16:54:38 GMT -6
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Post by Steamy Williams on Jun 27, 2016 9:06:13 GMT -6
Was the ADR Compex a diode bridging? The ADR Compex is FET based, not diode bridge. |
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