Wednesday, July 6, 2011

Patch Breakdown: The Prophet Piano

Today I'll be breaking down a patch for you guys.  This was one of the original intentions of the site, so hopefully this will happen more often from now on, since patch building is essentially the heart of synthesis.  You can have a great synth with crap sounds if you're not careful.  I didn't create this sound but I'd like to start with it as a template to what the future of this will look like.  Above is the Prophet Piano patch (No. 77 on my DSI Tetra) playing Mozart's Sonata in C (MIDI from this website).  I think it's a decent stab at the sound of a real piano, and should be easily recreated on any number of synths.  Hopefully this tutorial will give you a really great understanding of what is happening in this sound.

When you load up the editor and select this patch, this is what it shows you.  This is the simplest image to recreate the sound from, which is why I've included it first.  I'll break down piece by piece what every part here means.

Here's an in depth break down of what is happening with the oscillators.  Oscillator 1 is a slightly flat C#5 freq, with a pulse width of 16 (pulse width of 50 is a square wave).  You can also note that this is synced to the other oscillator, which allows it to have different harmonic content then the other oscillator but stay in tune with it.  Deselecting the sync makes the two waves have two different frequencies, so they sound like two different keys being played, which is not what you want for a piano sound.  C#5 tells us that when we play a C2, a C#5 will trigger from that note, and transpose accordingly.  This first oscillator is basically responsible for the higher tone of the sound.  Making it a pulse makes it a bit more hollow, which allows the other oscillator to come through better.  The mix parameter is set to 97, which means that we're mostly hearing oscillator 2 (purely oscillator 2 is value 127.)  Note the keyboard selection is checked for both of these, which means it varies depending on what note of the piano you are pressing.  Unchecking this would only be ideal for sound effects.  There is also no glide in the sound, because you simply don't want your piano notes gliding together.

Oscillator 2 is set to be a saw/triangle wave.  If your synthesizer does not have this, a sawtooth will have to suffice.  There is no fine tune here, which keeps the oscillator nicely in tune with the rest of your music.  The saw/triangle gives us a nice mix of the brightness of the sawtooth and the flute like bass end of the triangle.  Osc 2 is set to C2 which means when we play a C2 we get a C2 out from this oscillator.  You should always keep one oscillator set to the correct key of the scale for your patch, otherwise it would be very confusing.  Because the mix is set at 97, we hear more of the saw/triangle then we do the pulse wave, which gives us a nice reference that the C2 is the note we are playing, and keeps most of the harmonics made by Osc 1 more faint, but like a piano.  Again, there is no glide, and no noise is created (noise is used mostly in percussive sounds and sound effects.)  Over on the right side of this panel, we see the options for Osc slop, which is something DSI has put in to give us a more analog feel.  This is a subtle effect at best, so you won't be able to hear it much at 1.    There is no sub-oscillator presence and no feedback gain or volume.  These are used for more complex sounds.

Moving along, we now look at the low pass filter.  The frequency is set to 75, which is a little less than mid way.  This means that many of the higher frequencies will be cut off.  You may need to change this accordingly on your synth, as this parameter varies greatly among synths (as do all parameters.)  Resonance at 25 gives us some more treble.  Resonance is used to highlight where the cutoff is in a sound, but if it is taken too high, it begins to self oscillate, which is sometimes good when intended by usually bad for this sort of sound.  The resonance here is added to purely give the sound more high end.  Envelope amount is the amount the envelope (pictured on the right) affects the filter cutoff frequency.  A value of 8 means that it does not affect the cutoff frequency much.  Please note that while that parameter looks nearly halfway, it also has negative values, meaning the envelope looks like a negative version of itself.  Also to note here is the velocity value, which means depending on how hard we press the keys changes the cutoff frequency.  Pianos sound brighter the harder we hit the keys, and adding brightness  to a sound means turning the cutoff frequency higher, as brightness is considered the high harmonics.  If we press the keys lightly, we get a duller sound from the piano patch, which is more like a real piano.  Key amount is set to 16.  Key amount is how much the cutoff is affected by what note we are pressing.  The higher we move up on the piano, the higher the cutoff frequency is set because of this parameter.

Moving further, we see that the filter is set to 4 pole, which means that the higher harmonics past the filter cutoff are attenuated fairly heavily.  A 2 pole filter means they are less affected by the filter.  This type of filter makes more sense for this patch, based purely on using your ears.  Moving on to the envelope, we see that there is no delay for the envelope to take place, and the attack is set to 0, and the decay is set to 1.  This means that as soon as the note is pressed, the filter cutoff jumps to its sustain value because there is no delay for the envelope to happen, the attack is instantaneous, and the fall after the attack is near instantaneous as well.  The sustain value is set to 86, which is again set purely by the listener's ear.  You will likely have to change this value to be close to my sound, but it would be better if you found what you prefer.  Finally, the release is set to 83, which is reasonably high.  This means after I take my finger from the key, the filter cutoff slowly drops.  This is a nice representation of how the dampers return to the strings on a piano and silence it.  Setting this value to 0 makes the release part of the sound muffled, because the cutoff drops too quickly, and the rest of the sound is still going.  Finally, audio mod is a parameter that takes oscillator 1 or 2 (I forget) and modulates the cutoff frequency with it.  Again, this is mostly here to add a little high end.  Removing it, since most of you probably won't have this parameter, doesn't affect the sound much.

Still with me? We now have reached the amplitude envelope, or in laymen's terms, the volume envelope.  Setting the VCA level to 2 isn't important.  This should probably be set to 0, but is most likely there to try to simulate any strings still vibrating.  Turning VCA level to it's max value on the Tetra makes the sound ring out forever, so it's best kept so that the sound can actually decay.  Envelope amount is set to 127, the max, because we want to be able to change the full spectrum of the volume of the piano.  Velocity is set to 0 because we don't' want how hard we press the note to affect how loud it is (even though in some cases, this may be more realistic).  The delay is set to 0 because we don't want a delay before the volume is affect.  Attack is set to 0 because on a real piano, the piano is loudest as soon as the hammer strikes, much like an attack of 0.  The decay is set to 127 and the sustain is set to 1.  This means that when we press the key and hold, the sustain level is so low, that when it finally reaches it it is essentially 0.  This is much like a real piano, because you can press the key and hold it down, and the string will eventually stop vibrating even though you're still holding the key.  The decay level being set so high means that this will very slowly happen, much like a real piano.  Note that we're going to later modulate this setting, but it's important to understand the concept.  The release value is set to 38, which means that if we let go of the key before it reaches the sustain level, it will drop to no volume much quicker than the decay.  This is, again, like a real piano (I feel redundant) because this is when the damper returns to the key and silences it.  This happens quickly after you let go, hence the value of 38.  Finally, the last two parameters here are volume, set max (no other value would make sense) and pan, which changes slightly how far left or right we will hear the sound.

If you've made it this far, you're almost there!  Creating sounds is much quicker when you're not reading them off a page.  We now move to the modulation section, which basically is where we decide how something that has happened or is happening affects another part of the sound.  First off, we have the Note Number (mod source) changing the Envelope 2 decay (destination).  Envelope 2 is the amplitude envelope.  What this is doing is taking the note we're playing and changing how quickly the sound fades as we hold it.  On a real piano, the higher notes don't vibrate as long, so pressing the highest note on a piano only holds for a second, if even.  Pressing and holding the lowest note, same velocity, yields a much longer, slowly decaying note.  This is what this modulation is performing for us.  Now, playing high keys leaves no sustaining sound, whereas playing the lowest basses hold long, especially if we are holding our sustain pedal.  We set this amount to 55 (again, there are negative values here) because we don't want to overdue it and have the highest notes only click.

Moving onward, we have the note number (again, where we are on the piano) affecting the oscillator 1 frequency.  I'm not sure how the science works behind this, but I'm sure it's modeled after a real piano somehow.  Again we change where we are on the keyboard and it changes the frequency of oscillator 1 slightly.  The amount here is a very low value of -2.  Our next modulation source is the note number affecting the low pass.  Again, like before, this is showing that the higher notes affect the filter cutoff.  Finally, the last piece is having the note number change the envelope 2 release, which again is for the higher notes of the piano that lack dampers.  The other two control parameters are purely optional, giving you the ability to add a modulation to the frequency of the piano, and the mod wheel changing the filter cutoff.

I hope you've enjoyed this patch break down, and do not hesitate to contact me if you have questions, as I'd love to update this article and have it be clear as possible.  Hopefully these patch breakdowns will happen more in the future.  Enjoy!


  1. Hi Matt, thank you very much for your example how to create a piano sound.
    I own the prophet 12 and I searching desperately for examples in the internet, because this is my first synth
    and after 6 week practice I´m still a litte helpless to create bread and butter sounds like strings, piano, sax aso. So I followed you instructions, but what I have in the end was a astonishing siren sound??? Interesting. The problem was the destination LFO?? Can you hel me? thanks, take care CHARLY

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