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Distortion on FX inserts with Focusrite Scarlett 18i20

Posted: Thu May 01, 2014 12:45 pm
by dannym
I'm evaluating Forte trial (3.2 build 12.3072), 64 bit, on a Molten Music Technology Performer XL laptop running Windows 8.1 Pro. My interface is a Focusrite Scarlett 18i20.

Instrument plugins, both 64-bit and JBridged 32-bit, work fine. But I'm getting distortion whenever I insert any FX plugin (I've tried a few) on a module - not the kind of glitching you get when (for example) buffer sizes are too small, but a a continuous crackling/fuzz of the sound, which goes away as soon as I disable the insert. Sometimes, I get a loud, continuous (distorted) tone generated instead. Sometimes the problem happens as soon as I start up Forte and load a rack; sometimes it's OK at first but then happens for no apparent reason. Well - it seems always to be when I perform some action in Forte, rather than completely out of the blue, but it can be different actions and seemingly unpredictable. One example: I was running with an FX insert without problem, but got a loud continuous tone as soon as I saved the rack for the first time.

I have applied the usual recommended Windows tweaks for audio work - CPUs fixed at max rate, no core parking, USB sleeping disabled, wireless off, etc. I've tried playing with buffer sizes and using different USB ports and cables, to no effect.

I usually run at 44100. One thing that does stop the distortion temporarily is to change that to 48000 in the Forte preferences. It asks me if I want to restart, to which I say yes. Interestingly, when restarting I get a couple of error messages:
ASIO Driver "Focusrite USB 2.0 Audio Driver" reported an error: ASE_InvalidMode
Mixer Start: IMediaControl -> Run() failed with 80004005
and there is no sound from the Focusrite. However, I can see (using the Focusrite MixControl software) that it has indeed been switched to 48000. If I exit and restart Forte, the distortion or loud tone is gone. Typically, it stays gone for much longer than at 41000, but eventually returns.

I use the Focusrite at 44100 with Pro Tools 10 and 11 without any problems.

Finally: I've tried using an Avid MBox (3rd gen) at 441000 instead of the Focusrite. So far I have not had the distortion issue with that, but I have had the loud continous tone. (I used a rack and saved it without a problem, but when I stopped Forte and restarted it with the same rack, I got the tone.)

Any help/advice would be greatly appreciated. I'd love to buy Forte, but can't use it for live performance with this issue unresolved.

Re: Distortion on FX inserts with Focusrite Scarlett 18i20

Posted: Thu May 01, 2014 12:46 pm
by dannym
I should also add that I experience no problems using any internal FX that instrument plugins have.

Re: Distortion on FX inserts with Focusrite Scarlett 18i20

Posted: Thu May 01, 2014 4:06 pm
by dannym
Another guy is having similar issues with a different Scarlett model:

I've done some further testing. At one point, it seemed like the distortion got better the more I increased the ASIO buffer size in the Focusrite. (The choices there are from 1ms incrementing up to 20ms.) And that maybe the loud continuous tones tended to happen when that buffer size was smaller. However, the situation then became more confused, so I can't guarantee that is actually the case. (In any case, I was still hearing some distortion with the buffer up to 15ms. which wouldn't be acceptable anyway.)

I *have* managed to find a built in FX in an instrument plugin giving me distortion problems - the Mark 1 instrument in the Scarbee Vintage Keyboards for NI Kontakt. Switching on the autowah there gave distortion.

Latency: The DPC Latency Checker gives erroneous values for Windows 8 (see the web page), so I can't use it. However, the following shows I don't have a latency problem with my setup anyway.

I thought I would check the plugins I was having problems with in Pro Tools 11 as a comparison. Two examples where I was getting distortion in Forte:
Tape Delay effect in NI Guitar Rig 5 (FX Insert)
Autowah in NI Kontakt/Scarbee Vintage Keyboards/Mark 1 instrument (built in FX)

I had absolutely no problem running these in Pro Tools 11 at 44100 with the Focusrite buffer set to 2ms. But of course it was running the AAX rather than the VST versions. So I also loaded Blue Cat Patchwork - it's an AAX plugin which is a VST host amongst other things - and loaded the VST versions of Guitar Rig and the Scarbee Mark 1 into that. Again, no distortion experienced.

So.... Pro Tools/Patchwork can run the same VST plugins, using the same (Focusrite) ASIO driver, interface and hardware, as Forte, but doesn't exhibit the distortion problem. That leads me to suspect it might well be something to with the interaction between Forte and the ASIO driver...

Is there any other info I can provide you with, Mike? I'd love to get this issue sorted, buy Forte, and use it for upcoming live work!

Many thanks

Re: Distortion on FX inserts with Focusrite Scarlett 18i20

Posted: Fri May 02, 2014 10:12 am
by dannym
LatencyMon shows "green" on my system. It doesn't show anything noticeably different when I experience the distortion issue.