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PreenFM2 / Harsh noise at 13,5kHz from preenFM2
« Last post by Specter on May 11, 2017, 01:24:43 PM »

I have recently bought preenFM 2 and there's one thing that bothers me a lot - my unit produces a constant, very thin but loud noise at 13,5kHz.

Here's how it looks on a spectral analyzer:

This is of course very easy to filter out completely due to nature of the noise, but only on digital EQ's using a computer. Not so easy in hardware-based setup though and the sound is very harsh and unpleasant to ears, especially on headphones.

The noise seems to be independent of filters (I tried to put 4 separate filters on every instrument), volume knob (volume does not affect produced noise in any way) and also of power supply (appears on both USB power and DC - might be a tiny bit louder on USB but it's not a big difference 2-3dB tops - you might notice it if you look closely at the spectogram on the left side of my screenshot - this small peak is when I plugged USB cable in. Low noise appears across the whole spectrum after USB cable is plugged in, although much much lower than this 13,5kHz peak).
It also does not change at all no matter what preset is playing and how many parts are in use.

Overall I'm very happy with the instrument and I think Xavier did a WONDERFUL job in designing preen's interface, this is the very first hardware FM synth that I find accessible and actually fun to use. I would love to keep this device but currently this noise bugs me a lot.

Do you have any ideas what could be the reason here and can you tell me how I could possibly fix this issue?

Thank you!
PreenFM2 / Re: Stm32F4Discovery port
« Last post by norbim1 on May 11, 2017, 12:24:53 PM »
Hi Xavier!

Thanks for the tip. I just checked the symbol list, and found, that at 08041AC0 there is the OTG_FS IRQ handler, and thought that the 0x28041AC0 dumped PC value can be the same with a memory mapping offset. I'll try to find it with gdb, though I only used it before to debug a connected target.
PreenFM2 / Re: Stm32F4Discovery port
« Last post by Xavier on May 11, 2017, 09:38:27 AM »
The goal of this register dump is to be able to find where the firmware crashed.
I'm away from my dev computer and I don't remember exacly the steps to debug.
The PC (program counter) value is where it crashed.

With a mix of gdb, elf binary, 'layout split' or asm, and a gdb function to go to the PC value, you should get the C++ line where it crashed.

PreenFM2 / Re: Stm32F4Discovery port
« Last post by norbim1 on May 10, 2017, 08:06:59 PM »
I think it can be a problem with the USB stick or the power line to it (the PC number shows that it hangs on the USB OTG_FS IRQ handler). Check the USB stick, or the lines going to it. If all goes well, try to filter the power lines near the USB stick socket.
PreenFM2 / Re: Stm32F4Discovery port
« Last post by electron libre on May 09, 2017, 08:20:10 PM »
Hey norbim1

After sever tests, the STM is still freezing, either playing or idle. Is there something I can do to assist you?

PreenFM2 / Re: Stm32F4Discovery port
« Last post by norbim1 on May 09, 2017, 06:27:20 PM »
Let's try with latest firmware. The only drawback is that in the mean time I changed my encoders, so with this they work with reverse turn direction. Either change your encoder A-B pins connections or let me know and I'll build a new .bin in a few days.
PreenFM2 / Re: Stm32F4Discovery port
« Last post by electron libre on May 09, 2017, 02:40:16 PM »
Hello Norbim1,
After a small pause on this project I managed to get it running. I enjoy the clear FM sound and the very nice presets.

Now I have some stability issues. After a random Interval of time, from 10 to 60 secs the synth freezes. This only occurs with the 205 firmware, at least I do not remember to have it running the 106 version. The error code on the LCD is never the same. I play the sent by usb midi, USB powered. The usb voltage is about 4.5V. Is this an issue of the over clocked version?

Best regards, and thanks again for this great synth!

PreenFM2 / Re: New slippers -> no USB
« Last post by Xavier on May 09, 2017, 02:20:58 PM »
Cool  :)
Thanks for the update...
PreenFM2 / Re: New slippers -> no USB
« Last post by bigsecret on May 09, 2017, 12:56:29 PM »
Thanks Xavier

The new preenF405  arrived this morning and my Preen is once again visible as a connected device on my PC  :D

I now have a "spare" CERB40 which works just fine as long as you don't want to use the external USB port.

If I'm not careful I'm going to be building another one for my brother-in-law who wouldn't know what to do with the USB port anyway.

PreenFM2 / Re: Simulating Karplus Strong with PreenFM2
« Last post by keston on May 08, 2017, 10:13:40 PM »
Of course, Xavier! It's always a pleasure when I get to do sound design with my PreenFM2!
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