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PreenFM2 / Re: Share your creations using the PreenFM2!
« Last post by SMF on July 14, 2019, 06:45:21 PM »

so I have played with my preenFM2 this weekend, too. I think the result is quite decent for a first attempt in creating new FM-patches after some years now...

I hope you have as much fun listening to it as I had when I created it. And, Xavier I really love this little synth -- albeit I must admit, that I have not a too good understanding of how to manage banks in it. But...

many thanks!
PreenFM2 / Re: Basic waveforms with FM
« Last post by SMF on July 12, 2019, 01:28:19 PM »
Hello again,

I have made a measurement of the preenFM2-output (noise is due to digital amplification to make it fit the simulated data in gnuplot. Despite a 13-16 kHz whine at -60dB -- the OLED? -- the output is dead clean) and compared it to

a) a 3OP-PM sawtooth-approximation without a phase-shift in between the carriers and the modulators


b) a 3OP-PM sawtooth-approximation with a phase-shift of pi*0.5

One clearly can see, that (b) is quite close to the output of the preenFM2. The differences -- I think -- mostly come from the frequency response of my audio-equipment which will of course distort the signal a little bit.

This should clarify what I meant with "phase-delay" in the last postings.

To explicitly say this: Both variants (whith and without the phase-difference) absolutely sound the same and have the same spectral distribution. Only the waveform on the oscilloscope will differ from the expected result. So, basically this is nothing to worry about...

On the other hand side: This result makes me really think that it might be a good idea to (maybe via a flag for backwards-compatibility?) switch the preen over to use PM (as most (all??) other "FM" synths do). It's using PM anyways, now...
With this change it would produce the expected waveforms from the various tutorials and it would (most probably) save some CPU-time to calculate...

For me personally it was just irritating. The sound and the flexibility of this nice little monster is outstanding! I love it, so many thanks Xavier!

all the best,
PreenFM2 / Re: Basic waveforms with FM
« Last post by SMF on July 11, 2019, 11:06:25 PM »

after some further experiments... Could it be that there is a highpass-filter in-between the carriers and the modulators (in-between every modulator-carrier-link... so there should be quite a lot of them)? This could explain the observed phase-shift. And if so, this would effectively implement phase modulation instead of frequency modulation because of using the derivative of the modulation-signal, then.. wouldn't it?

If I'm not missing a point here, wouldn't it be "better" in this case to directly use PM and to save some CPU-cycles by avoiding the HP-filters (maybe to increase sample rate or polyphony or for allowing feedback)?

all the best,
PreenFM2 / Basic waveforms with FM
« Last post by SMF on July 11, 2019, 02:03:30 PM »
Hello all,

so I am the proud owner of a preenFM2 now... And I try to get accommodated with its FM-synthesis (this is not the first FM-capable synthesizer I use, btw...), so I thought it would be fun to do what I have done on many FM-synths before: creating baisc waveforms with FM (saw, tri, square, pulse) to get an understanding of it's parameter-range and response...

But whatever I try I can not even come close to a synthesized 2-OP approximation of a sawtooth-waveform?!? hmm,... The spectrum looks right, so I guess there is some sort of phase-delay inside the operators, maybe?

BTW: just curious, but what was the reason for not using phasemodulation but real FM?

many thanks,

PreenFM2 / Re: output routing
« Last post by Xavier on July 09, 2019, 09:29:26 PM »
...I just saw, that the two 12-bit channels of the MPC4922 are combined for the 18 bit resolution of the output. So my educated guess is: the PreenFM2 is two channel audio out by design.


But you can redirect one instrumnent to one mono channel and a second one to the other.
Go to the mix engine menu, then turn right or left one of your op while holding down the mid left button. That will turn all mix* at the same time.

PreenFM2 / Re: output routing
« Last post by Omnichordman on July 08, 2019, 09:38:19 PM »
...I just saw, that the two 12-bit channels of the MPC4922 are combined for the 18 bit resolution of the output. So my educated guess is: the PreenFM2 is two channel audio out by design.
So I think it would be easier and even cheaper to put two Preens in one housing, for 4-channel FM.

PreenFM2 / Re: output routing22
« Last post by Omnichordman on July 08, 2019, 09:03:20 PM »

I am pretty new to the Preen, and I have the exact same question.
From what I can see on the schematics, the two DAC outputs on the MPC4922‘s, are summed to one op-amp each, so there would at least 2 more op-amps be needed.
I don‘t know if SPI_DAC1 and 2 can send stereo-Data, or if two more SPI_DAC‘s are needed.

Can anyone enlighten us?

PreenFM2 / output routing
« Last post by klangFM on July 07, 2019, 09:16:32 PM »
How can one  instrument play only at one mono output,
or how it can programmed to play all 4 instruments to 4 outputs individually?
I'm sure it works, but can't find it in Menu.
PreenFM2 / Re: custom extended firmware
« Last post by Alexey L on June 30, 2019, 06:02:48 PM »
Hello! Thanks for the work!  :)
But I tried an alternative firmware and found that the operators are working in free-running mode.  :o
And with its use, everything sounds much quieter.
This is normal?
I really wanted the operators to work with a fixed phase, as in the standard firmware, in order to use Preenfm2 as a 8 parts percussion module.  ::)

I did a test to show the difference.
First, the standard firmware plays.

PreenFM2 / Re: Random patch resetting - was yellow oled issue
« Last post by Road_Kill on June 29, 2019, 06:18:16 PM »
Xavier - Apologies for not replying sooner as this was a busy week. While I initially said I wouldn't be opening up the synth again until about this time, in fact I immediately turned around after my last reply and opened the synth back up! (Because who needs sleep when you could get a PreenFM up and running?)

The first thing I realized was that things were a lot more cramped with the insulated ground plate under the OLED than I initially thought. One consequence was that the wire coming from MCLK patching the defective trace was mashed such that it was possible intermittent shorts could occur with adjacent pins. And while I didn't see any evidence, I couldn't rule out random shorts occurring with solder joints piercing the insulation of the grounded shield. So I covered the circuit board under the shield with a layer of electrical tape, paying extra attention to really isolating the wire tacked to pin 6 of the 405.

I have been running the synth continuously since then, with and without sequencers running for many hours, and with as much hands-on as the past few days have afforded me. I think it's safe to declare this synth operational! So yes, it took you telling me to look at pin 6 to actually consider that might be the problem despite the big ugly wire hanging off of it. :P But now I've hopefully made the synth robust and if not, I know where to concentrate future improvements/modifications.

Once again,
Thank You!
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