Audio Output from SMD version

[ericd]

Hi, new forum member here.

First, the Preen FM2 is fantastic, thank you Xavier and everyone else who keeps developing new features.

However I think I made a mistake, I jumped in and bought a pre-built SMD version without being aware of the differences. I have linked a recording of a single sine wave, 1 voice, with no modulation and all other operators off. There is a noticeable 'phaser' sound especially as it fades out, that I don't think should be there with pure sine wave (other synths sine waves don't have this sound).

https://soundcloud.com/user-335915384/preen-output

I also tried splitting that sound file into separate mono tracks and it is audible on both sides.

Is this normal for the PreenFM2? Is this maybe a problem inherent in the SMD build and specifically the use of a single audio output jack? I don't think it is aliasing as the digital processing should be the same?

The general functioning of the unit in terms of MIDI control and parameter settings all seems to be good.

Am I just being overly sensitive about the sound?

Many thanks

[solipsvs]

as far as i know the smd version is a branch made by a preenfm2 fan and xavier has nothing to do with it

[ericd]

Oh that isn't great. How can someone be selling a product called 'PreenFM2' if it has nothing to do with the developer? I get that it's open source but it doesn't seem ethical.

I knew before I bought it was a SMD version  but didn't know that meant it wasn't even supported. 

As for my unit, I guess I'll squeeze what I can out of it, and save for a proper PreenFM2.

If someone could compare the audio output of a single sine wave from a proper PreenFM2 to the output in the soundcloud link above I would really appreciate it.

Thanks/

[solipsvs]

it was made by an enthusiast.  there is a thread somewhere here so you could ask the maker.  where did you buy it?  i think its sorta unnecessary unless it costs less or shrinks the footprint or does something the through-hole doesnt do, even tho i was sorta fascinated when they announced it.  id love a preenfm2 wrist watch honestly!  with an onboard sequencer and a little speaker... and a space bar!

[ericd]

Thank you. I found that thread, I will try posting there but it hasn't been active for 2 years.

I bought it through the forums at Elektronauts. Who knows, maybe it's just one faulty unit. I'd love to hear from any other SMD version owners whether they get the same problem with the sine wave output.

Sign me up for that wristwatch!

[Xavier]

It's difficult to compare without knowing exactly what your patch is.

With the use of Velocity, multiple carrier operators, 4 instruments, several voices on your instrument, the resulting amplitude of one single sine wave can be very low.
So what you seem to hear is the granularity of the DAC.

The pfm2 DAC is 12 bits + 6 bits that are added with the usage of a divider resistor  bridge. Bad choice of resistors here can increase this effect.

Check with :
. Velocity 0
. Algo 1 (to have only 1 carrier operator).
. Instrument 1 : 1 voice
. Instrument 2,3,4 : 0 voice.
Is it better ?

This sound also should disappear as soon as you start increasing the modulator indices (IM).
If that's the case, stop focusing on a single sine wave and make real FM ! 

[ericd]

Hi Xavier

My patch is exactly as you suggest:  only a single carrier, all other OPs turned off, velocity at 0, no IM and no modifiers assigned in the matrix. Just a pure single voice sine wave.

Is the sound in the recording as good as I would get from a PreenFM2 using just a sine wave? I understand this is not really the intended purpose PreenFM2 and can get more pure sine waves from other machines. ( I just love the sound of pure sine waves!)

But I really just wanted to know if it was an issue with the SMD version, or with my particular unit. If it is normal behaviour then I can stop worrying about it!

[Xavier]

If you have only 1 voice and the other instruments have 0 voice (the DAC is shared between all instruments + all voices per instrument), this digital noise we can here is very loud.

[ericd]

OK, so it is related to what you said:

"The pfm2 DAC is 12 bits + 6 bits that are added with the usage of a divider resistor  bridge. Bad choice of resistors here can increase this effect."

Can I find the information somewhere on best choices of resistors to see if this is a problem?

[Xavier]

I just checked and I can hear that kind of sound with pure sound wave long release with my preenfm2.

The resistors are the 2x 115k and 1.8k on the picture here (near the mpc4922) :
http://ixox.fr/preenfm2/the-pcb-r5/pfm2_06/#main

115/1.8 = 63.88 (~64) = 2 ^6.
That's how the 6 bits of the second DAC are added.

[ericd]

OK thank you Xavier. Sounds like it's normal. I appreciate your help!

[solipsvs]

xavier...  any plans for an fm wrist watch?

[Drexy]

Hi

I just ordered a SMD version before looking at this forum, is the SMD version bad? did I make a mistake?

[Xavier]

Hi
I just ordered a SMD version before looking at this forum, is the SMD version bad? did I make a mistake?

Hi,

I'm not aware at all of these SMD versions, the author never contacted me for anything.
I really think that half the fun of the preenfm2 is to build it yourself.

Xavier

[ericd]

It's "bad" from the perspective that Xavier developed the PreenFM2 and then someone else used his work to develop a different version without his approval. Unfortunately it is hard to know that without a bit of investigating.

The person who made the SMD version did actually make a thread on this forum.

In theory I agree 'building it is half the fun' however not all of us are physically able to do that so I don't think it's fair to imply someone should not have the chance to use such a great synth. I think people who are 100% physically capable easily forget that not everyone is so lucky.

The SMD unit itself is fine, Xavier said in this thread that the sound issue I was worried about is the same on the original version.