Author Topic: Aliasing noise?  (Read 1270 times)

t

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Aliasing noise?
« on: June 01, 2014, 08:28:19 PM »
Just finished assembling the kit and am now playing around with my PreenFM 2 for the first time. I really like the sound and the user interface; very well done! :)

There seems to be a fair amount of what sounds like digital aliasing noise in “softer” sounds when notes are played at a lower velocity. Should I consider this normal, or could this indicate a build error I might have made?

Xavier

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Re: Aliasing noise?
« Reply #1 on: June 01, 2014, 09:29:43 PM »

Hi, it's always nice to hear about a new built. Congrats :D

Does the 2 channels (right and left) sound the same ?
It can be a problem with the DAC summing.
The output of each channel is the result of a 12 bits DAC and a 6 bits summed by the 115K and 1.8K resistors... Check the values and the soldering points.
If the resistors are wrong, you'll only enjoy a 12 bits DAC with much more digital noise.

But even with 18 bits, you can hear digital noise at low volume in some cases.

To minimise the noise, try to set only the voices you use.
Set voices to 0 for instrument you don't use.
Don't set number of voices to 16 is you only use 3 or 4.

In adition, "Velocity" was added for this reason in preenfm1.  You can try to lower a bit the value.
Last thing, check that the "mix" values are not to far from 1.0.

The goal of all this is to have a good use of the 18 bits.

Xavier

Mmarsh

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Re: Aliasing noise?
« Reply #2 on: June 03, 2014, 09:34:01 PM »
One more tip: use the filter to round off the top a bit.  Works nicely with some patches :)

t

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Re: Aliasing noise?
« Reply #3 on: June 04, 2014, 07:23:54 PM »
I’ll check my soldering, but it seems that what I’m hearing is considered normal. :)

I already figured out that lowering the number of voices reduces the issue, but it can still be rather noticeable in the decay part and when you’re playing softer passages.

The filters are great, and really add to the sound design possibilities, but using a bit of low pass filtering doesn’t seem to reduce this particular issue at all.

t

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Re: Aliasing noise?
« Reply #4 on: June 05, 2014, 09:08:06 PM »
And here she is in her metal case:



I used a dark contrast glass below the cutout instead of the transparent plexi that comes with the case. It looks really sexy with the OLED display. I also decided to use the hex screws that came with the original plexi case, instead of the small black ones.

In case anyone wants a replacement glass for the metal case and/or a parts set for the original case (plexi without assembly materials); just let me know, I’d be more than happy to send it to you.

Xavier

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Re: Aliasing noise?
« Reply #5 on: June 05, 2014, 09:38:03 PM »

Wohoo... nice  8)

Xavier

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Re: Aliasing noise?
« Reply #6 on: June 05, 2014, 09:39:19 PM »

But how did you screw the hex m3 screw in the m2 14mm spacers of the metal case ?

t

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Re: Aliasing noise?
« Reply #7 on: June 05, 2014, 10:07:06 PM »
I used different spacers.  8)