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Messages - Xavier

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PreenFM2 / Re: Frequency
« on: December 09, 2017, 11:29:51 AM »
Even with 16 you'll get into aliasing (noise) very quickly.
It's a frequency multiplier.

If you play a C6 note (~1000Hz) with 16 you'll get 16Khz base frequency.
With all the harmonics brung by the modulation you'll very very quickly reach the limit of the 40Khz sampling rate.

40Khz sr -> frequency above 20K will be folded back bellow 20k and will create kind of digital noise.
That's maybe what you want bu i think 16 is enough for that.


PreenFM2 / Re: (compatibility?) questions
« on: November 30, 2017, 07:19:23 PM »

1) You do that with the preenfm by modifying the MI (modulation indices) between operators.
For the carrier operator (lower level, their output is the sound) you modify the MIX parameters.

2) Use the matrix and targets the o[1-6]Fq params. They are the operator 1 to 6 frequency.
Use o*Fq for all at the same time.

3) They both modify the operator frequency. Harmonic is when you want the same number of semitone bellow and above the base frequency.
The other one exists for a longer amount of time in the preenfm2 and is a simpler frequency multipler so you won't have the same interval above and bellow the main frequency.
Harmonic is the typical one to use for pitch bend source.


PreenFM2 / Re: Hiss
« on: November 28, 2017, 09:38:46 PM »

Try to maximize the bit resolution for your instrument.

Chose the number of voices you need, not more.
Try to set 0 voice to instrument you don't use.

Modify "velo" to see if a lower value improve the result. What it does is the minimal velocity will be higher so the wav bigger and the resolution better.


PreenFM2 / Re: Vishay OLED brightness
« on: November 26, 2017, 10:15:43 PM »
my tech has them in his tx802 and tx81z at full brightness and was looking to try to find where the limiting resistor that is on the rev c pfm2 PCB...   there isnt one?

What limiting resistor are you talking about ? I don't get it.

A small update : I put today a 2x40 white oled in my ambika and it works great.

I have no idea what the problem is with th 4x20 white OLD in the preenfm2. I'll update this thread if i find something.

PreenFM2 / Re: preenfm2 editor 2.08.4 (November 25th 2017)
« on: November 25, 2017, 05:08:54 PM »
Audio Unit for mac is available with 2.08.4 as well as a couple of new stuffs:

PreenFM2 / Re: Vishay OLED brightness
« on: November 25, 2017, 12:31:29 PM »
so is there a resistor that can be changed so this display is as bright as other colors?

No, white oleds are much less bright.

PreenFM2 / Re: PreenFM2 SMD version
« on: November 22, 2017, 09:00:02 PM »
Is there any reason you've chosen a non standard sampling rate? Instead of 42031.52 (1142 ticks) you could have gone for 44117.65 with 1088 systicks.
In any case 42KHz is just 5% away from 44.1KHz so I expect the internal PCM5102 PLL to lock.

It's only a performance reason.
With those sample rates, the CPU is close to 100% in worse case scenario (full polyphony with the most demanding FM algo, FX, arpeggiator..).

PreenFM2 / Re: Latest firmware : 2.08a
« on: November 20, 2017, 11:08:43 PM »
what about pressing the inst button and pressing an encoder down, or inst and menu?

Maybe you said it, i don't remember.
But why do yout think it's a good idea to have the midi channel in the preset ?
Don't you have your synth/sound module with a dedicated midi channel each ?

PreenFM2 / Re: Latest firmware : 2.08a
« on: November 20, 2017, 09:10:47 PM »
with the recent activity in the firmware i think it would be a good time to implement the combo settings page after i4 (i8 respectively  ;) )
did you do any thinking in that direction? as i said before i think most crucial settings will be:
midi channel for each instrument
midi offset, transpose +-48 semitones all incoming midi on an instrument

I thought about this and i thought it makes the UI more complicated and less consistent.

PreenFM2 / Re: PreenFM2 SMD version
« on: November 20, 2017, 09:07:35 PM »
I have a few issues to clarify:
- what is the crystal you are using for the F4? I've put a 12MHz one, it needs to be a divisor of 48MHz because of the USB

I also use a 12Mhz on the preenF405.

- right now I've connected Channel1 Left/Right to one stereo jack AF1 and Channel2 Left/Right to AF2
  would it be better to have Channel1 connected to both AF1/AF2 tips and Channel2 connected to both AF1/AF2 rings? This second configuration will allow the use of only one PCM5102 and allow the use on mono cables as before.

With solution1 mono cable will be possible but we'll need 2 PCM5102 even for 2 mono channels, right ?
So the difference is small, i don't have a strong opinion.

- because I'm mixing the 2 lefts and the 2 rights for the headphones amp there is a small (-43dB) signal crosstalk between the before mentioned channels. If one doesn't want this if should replace R30/R38 with 0 ohm resistors and not solder the TDA2822M and its capacitors.

- a very important issue is the output sample frequency. The PCM5102 has its own PLL which locks to the WS signal. If the F4 isn't able to provide a constant stream of data this might be a problem. The F4 can also generate instead the system clock and send it to PCM5102 (just 2 extra pins of F4).
- there is an error between the desired sample rate and what the F4 can provide with the current crystal - for example instead of 44KHz the real audio frequency is 43.4KHz (an error of 1.35%). A 6% error is already a semitone. I haven't studied yet the current firmware - is the software able to compensate for this? what is the sampling rate you are using now?

I don't know the PCM5102 so i don't know what is best for it.

Sample rates are here :
I have a firmware (with o suffix) which overclock the F4 to 192Mhz which allows a higher sample rate.

With the current firmware the F4 has to feed 4 DACs so there is an interuption 4 times per sample to deal with DACs :

This interuption takes the sample data from a 192 samples buffer that is constantly fill  by  synth.buildNewSampleBlock() :

- 24 and 32 bit samples need to be loaded in the SPI data register twice because that's only 16bit wide in I2S mode so the best way would be to DMA the data from the memory and let the MCU do something else in this time

Yes, would be nice.

PreenFM2 / Re: PreenFM2 SMD version
« on: November 20, 2017, 04:15:54 PM »
It works but i read from several olde display manual that we should avoid sending 3.3v data to a 5v powered display.
Do you think it would be better to convert the LCD_* lines to 5v (with a 5v inverter or anything else)?

PreenFM2 / Re: PreenFM2 SMD version
« on: November 20, 2017, 09:52:22 AM »

And you will solder all these SMD components by hand ?  :o

PreenFM2 / Re: Latest firmware : 2.08a
« on: November 20, 2017, 08:04:24 AM »

PreenFM2 / Re: PreenFM2 SMD version
« on: November 19, 2017, 11:47:35 AM »
I don't get exactly how the firmwares flashing will work.

Is there still the JMP3 to flash the STM32F4 through USB ?
Will the STM32F1 flashing require the ST-LINK programmer ?

Would be great to have also a led for the STM32F1, so that we can make it blink a little when the board is switched on to check it's correctly flashed and working.

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