Hi

I've found a pdf containing pictures of all the waveforms and wavetables the PPG wave synthesizer used, it's quite good really as I have wanted to build a PPG in Pure Data for a while, but I didn't think such a resource existed.

I have two questions
1. I have never really used pictures and visuals in Pd before, so I was wondering if it would be possible to take the picture of a waveform from the pdf and write it into a table in Pd, and then hopefully save it?

2. If this is possible, then I would like to build the wavetable, which from what I gather is just a list of waveforms that are added together over time, then played back at a given frequency. Is this possible, and if so, does anyone know of any good tutorials that would give me an idea of how to do it?

This is going to be my summer project, I might even try my hand at modeling the PPG filter then compiling it in C, although that is running before I can walk

I have attached the pdf for anyone interested in PPGs or wavetable synthesis in general

Cheers!

EDIT- I realised whilst I was uploading the pdf it was 2.5MB, which is a lot to stick on this site, so here is the link I got it from
www.seib.synth.net/documents/PPGWTbl.pdf

Hi

here is a patch built by Tom Erbe, using waveshaping techniques with sinesum; it will be for your second option though.

I hope it will help

http://www.pdpatchrepo.info/hurleur/Midi_Hammond_like.pd

Yop,

today I've been searching on the web for some "bit crushing" or "pseudo ring mod" fx pedal.
I found one which is my favorite, but this gave me the taste for emulating such effects on Pd first. Two simpler models encountered along my search give some information :

• the first one gives some info about how carrier frequency is used : http://www.catalinbread.com/Heliotrope.html
• the second one gives some wavetables, similar to those of LittleRedCourgette : http://www.wmdevices.com/GeigerCounterCivilianIssueManual.pdf

Those info are raw, and I don't know whether they can be crossed together, as they deal with different devices.

I'm new to PPG so I'll start reading again Pd's tutos over wavetables, browse the forum and report. I'm joining you, LRC ! Our goals are different but could be complementary.

One of the main issue remains finding files of wavetables or 'extract them' from graphical info ...

Seeya,

Nau

Hello,

I've been thinking about how to capture the waveform data from the pdf.

If each waveform is copy&pasted into an image file of standardized size for this purpose, data can be parsed into Pd-readable form with help of GEM object [pix_dump]. This object sends the raw pixel data as a list containing RGBA data for each pixel. In a black&white or greyscale picture the RGB values are identical. With [zexy/tabset] the list can be stored in an array for further processing.

[gemhead]
|
[pix_image <your_waveform_image>]
|
[pix_dump]
|
[tabset <your_array>]

In the attached patch [pixdumptest.pd] image pixels are stored in a Pd array with the method described above. This is only a start.

For each pixel in a greyscale image, only one value is needed, so the array can be 'downsampled' to contain only the first of each four values. The resulting array has to be interpreted as x-y values. Because the lines in the pictures are very thick, there will be many y-points for each x. Now you need some clever way to decide which of these is representative for the waveform.

Katja

http://www.pdpatchrepo.info/hurleur/pixdumptest.pd.zip

sound

Patch [plotextractor.pd] shows how a waveform image is roughly converted to a Pd wavetable. I tried this with wave0 from the PPG pdf. Because of the wide lines in the original it is not yet very precise, and the patch needs to be refined to find the center of a line. Still the sound is not so bad, for a start.

It's funny to hear this sound in Pd now. Some twenty years ago, a friend owned a PPG synth and I was much impressed. It was a very special, expensive synth in those days. I hope you will succeed in building a Pd version of it, LittleRedCourgette! Let me now if the plot extractor works for you.

I have done this patch for 128*128 pix images, but it would be possible to translate it for 512*512 pixels for example, to get better precision.

Katja

http://www.pdpatchrepo.info/hurleur/plotextractor.zip

Thanxs Katja ! Seems good !
Thanx Beranger, a good starting point.

Cheers BerengerRecoules, the hammond one will come in handy when designing new waveforms for the synth.

I haven't had time to check your patches katjav, but they sond like exactly what I was after. I can still see myself having to fiddle about with them in something like paint, or the equivalent on Mac, so all the waveforms are at zero corssing at the edges of the tables.

I've got a lot of work on this week, as I have done the past fortnight, but when I've finished that I will get straight on it and post up my first attempt.

Also I will need to get my head around interpolating between waveforms, as this is how many of the wavetables in the ppg work, will also save disk space.

One upside is the PPG was known for aliasing, so I won't need to worry about bandlimiting the waveforms!

Nau, this was posted for bit depth reduction originally by Maelstorm

[expr~ $v1*.5+.5] <-put the signal in 0-1 range
|
| [8\ <-bit-depth
| |
| [expr pow(2, $f1)-1]
| |\
[expr~ int($v1*$f2)] \
\ |
\ |
[expr~ $v1/$f2*2-1] <-bring it back to -1 - 1 range

I used it recently in a waveguide guitar patch I built and it worked perfectly, I'm going to put in the the ppg emulation.

The page I found it on: http://puredata.hurleur.com/sujet-1214-bit-crusher
One of the posts further down the page has a bitcrusher attachment

There is also a ring modulator in the help browser in audio examples, I think there might be two actually. I don't really know how they work though, I can't draw any similarities between the help patch and a standard ring mod

sorry, that was the wrong post, I actually found a bitcrusher patch attached on a page about analogue overdrive
http://puredata.hurleur.com/sujet-1232-analogue-style-volume-levelling
it is on the second post from the bottom

Thanx LittleRedCourgette, I was already using a less sophisticated yet similar implementation, I'll update my patch immediately.

really cool idea. have you made any headway since the last time youve posted?

Real PPGs have a sample rate of 195313 Hz (I think) and use nearest neighbor interpolation (i.e. tabread~). All waveforms are 128 samples long (this is more important than the 8 bit amplitude quantization), and they're all summations of sinusoids, except for the algorithmically synthesized ones.

The abstractions I posted in another thread (http://puredata.hurleur.com/sujet-8135-new-anti-aliasing-phase-distortion-abstractions) help a lot for this kind of low resolution synthesis. You can get higher quality (in a good way) than you would from a real PPG.

I'm working on a real time additive synthesis engine that should help with generic low resolution wavetable synthesis, FM (like the Synclavier), and other things (waveshaping, formant stretching, etc.).