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Author Topic: Soundcraft Impact Gain Control Artifacts?  (Read 1328 times)

Dave Coulter

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Soundcraft Impact Gain Control Artifacts?
« on: April 22, 2017, 07:38:10 pm »

Hi everyone - I just demo'd an Impact and immediately noticed that there were quiet artifacts in the signal when turning the gain encoder. Present enough to be a no-go for me.  It was on multiple inputs, routed to multiple outputs, so it was system-wide.

With all the positive things I'm reading on this forum about the Si series, surely this is an anomaly?  The salesman didn't know whether that was normal or not, so I'm asking your experiences.  My work is live corporate and broadcast, and I have to make small adjustments in gain on live mics enough that my clients would be be going crazy hearing that.

Thanks in advance.
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Samuel Rees

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #1 on: April 22, 2017, 09:56:56 pm »

LS9s and M7s definitely do something like that. I've head some other consoles make a little something if you spin gain real fast. I have not used the impact myself so I don't know how severe it is, but it's not totally unheard of for there to be a small sound.
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Dave Coulter

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #2 on: April 24, 2017, 01:19:31 am »

Thanks Samuel. I know there are a lot of mixers on this forum who use the Si series. It would help me out a lot if any of you could weigh in on this.  Do you find the gain control to ever induce noise into the signal? Thanks.
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Samuel Rees

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #3 on: April 24, 2017, 09:18:18 am »

Thanks Samuel. I know there are a lot of mixers on this forum who use the Si series. It would help me out a lot if any of you could weigh in on this.  Do you find the gain control to ever induce noise into the signal? Thanks.

I have an an Si Compact and I mix on Expressions here and there. I don't explicitly remember whether or not there are any artifacts. I can test the Compact when it gets back from a rental today if I have time. Even Digico MADIrack pres make a little something when you spin them real fast IIRC... unless the sound on the impact is unusually severe I probably wouldn't worry about it myself.
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Robert Lofgren

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #4 on: April 24, 2017, 09:56:18 am »

This artifact is usually known as 'zipper noise' and is more or less present in all digitally controlled preamps.
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Jim Rutherford

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #5 on: April 24, 2017, 09:36:03 pm »

I've never noticed any 'zipper noise'.  SI Expression 3.


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Dave Coulter

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #6 on: April 24, 2017, 11:51:54 pm »

I have an an Si Compact and I mix on Expressions here and there. I don't explicitly remember whether or not there are any artifacts. I can test the Compact when it gets back from a rental today if I have time. Even Digico MADIrack pres make a little something when you spin them real fast IIRC... unless the sound on the impact is unusually severe I probably wouldn't worry about it myself.

My main experience with digital consoles is the QL1, M32, and the 01V series, which I don't think exactly apply to this.  I'm just talking about subtle adjustments... if I were doing radical fast movements I wouldn't expect it to be usable live anyway.  I don't believe I've ever heard "zipper noise" on the Midas or Yamahas.

If you get a chance to listen to the Compact I'd appreciate it, as I suspect most if not all of the Si's might have similar gain encoder behavior.  Thanks.
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TJ (Tom) Cornish

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #7 on: April 26, 2017, 09:36:26 am »

I don't believe I've ever heard "zipper noise" on the Midas or Yamahas.
The 01v series has analog preamp gain, so that wouldn't do it.  LS9/M7 definitely do - internal relays select different gain ranges for the preamp.  I haven't found it to be a problem in real-world situations as gain changes during the show are rare.
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Tim McCulloch

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #8 on: April 26, 2017, 10:06:33 am »

Hi everyone - I just demo'd an Impact and immediately noticed that there were quiet artifacts in the signal when turning the gain encoder. Present enough to be a no-go for me.  It was on multiple inputs, routed to multiple outputs, so it was system-wide.

With all the positive things I'm reading on this forum about the Si series, surely this is an anomaly?  The salesman didn't know whether that was normal or not, so I'm asking your experiences.  My work is live corporate and broadcast, and I have to make small adjustments in gain on live mics enough that my clients would be be going crazy hearing that.

Thanks in advance.

It's called zipper noise and it's based on the incremental "size" in dB of the gain steps.  The bigger the step the more obvious the noise especially if you move the encoder quickly.  There is no way around this and it's common to EVERY digitally controlled preamp regardless of brand.

What makes a difference is the size of the step and the speed at which you adjust the encoder.

What is worse - a signal that is too low or clipping - or a small noise?  If your clients are that picky you need to get a different (and likely much more expensive) mixer, possibly analog if you can't abide by this characteristic.
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John Roberts {JR}

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Re: Soundcraft Impact Gain Control Artifacts?
« Reply #9 on: April 26, 2017, 10:42:37 am »

Yes zipper noise from digital step size during gain control changes is generally only noticed when music is present. There is a design strategy to mitigate this, namely coordinate the gain changes with signal zero crossings, that way the gain change gets multiplied times zero for lower audibility. This clearly increases circuit complexity so isn't always used for every gain trim. Some premium digital mic preamp gain controls build the glue circuity to support ZC coordination inside the chip set to manage this transparently.

I have no idea what technology Soundcraft is actually using under the hood inside the Impact (mixer?).

A few years ago I spent some bench time working on a processor using digital pots for gain control. I expected zipper noise so designed in zero crossing capability, but never needed to turn it on because in general use the gain step artifacts were not noticeable (in my application, mostly speech).

Continuous musical tones at low level will probably be most noticeable during gain step changes, while the step size can also make a difference. Fewer larger steps will obviously be more audible than more, smaller steps (which costs more money too, I used a lot of small steps in my project). 

Do you experience these artifacts from faders, designed to be manipulated while listening to signal, or only on the gain trims? Maybe they don't intend for customers to mix on those trims? Covering a large gain range with only a handful of gain steps could be more audible. 

JR
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