Why some arp sounds play back notes differently every playback?

[Anne22]

Hi David. Sorry for disturbing you again. Why some Logic Pro arp sounds play back the same notes differently every time when I play back a project? For example, I like the arp sound called "Passing Through Tunnels". But every time I play back a project it may not give a version that I like.  Is there a way to fix this issue? Thank you. 

[enossified]

There's a few things going on in that Alchemy sound.

 

If you open up the Alchemy window, select Advanced and then select only source A. In the envelope window, select AHDSR 2. You should see this:

 

Two things jump out here:

The envelope is set to not sustain. If you turn off both the arp and the effects and play a note you will hear something like a click. It will sound different every time you play the same note.

Now look at the waveform for source A. Play the same note repeatedly and you will see that playback of the sample starts in a different location every time.

Now edit AHDSR 2 by setting sustain to the maximum. Select global and turn source 2 off.

Select source A again to see the sample. Now hold a note and you will hear the entire sample play back. It's a rhythmic loop!  Then turn the arpeggiator back on and hold a note. You can see how the start of playback of the sample is always different.

Then turn the effects back on and hold one note. The delay effect is syncopated (one channel 1/8 note, the other dotted 1/8 note) and the modulation effect is not tempo synched. What you hear is to the ear pretty random.  Play a chord, and it gets ever more random sounding.

Now set the AHSDR 2 sustain back to 0 and play a chord. It sounds percussive again, but even with a single note held, it still sounds pretty random.

So the notes played are the same every time but the sound coming out of Alchemy is not the same every time. Hope this helps explain what is going on here.

 

Edited March 20, 2023 by enossified

[scg]

Maybe enossified covered this and I missed it, but there's also some random sample-and-hold modulation in that preset (which affects, among other things, the sample start parameter). You'll probably find similar random modulation in other sounds that behave similarly. I'm not aware of a way to make that deterministic. If you wanted to really dive into the sound design, you could possibly replace the sample-and-hold modulation with a sequencer modulator or perhaps external automation, although making that change might not be entirely trivial...

A more prosaic solution would be to bounce it out until you get something you like, and then use that (although that would have its own disadvantages).

[Anne22]

21 hours ago, enossified said:

There's a few things going on in that Alchemy sound.

If you open up the Alchemy window, select Advanced and then select only source A. In the envelope window, select AHDSR 2. You should see this:

Two things jump out here:

The envelope is set to not sustain. If you turn off both the arp and the effects and play a note you will hear something like a click. It will sound different every time you play the same note.

Now look at the waveform for source A. Play the same note repeatedly and you will see that playback of the sample starts in a different location every time.

Now edit AHDSR 2 by setting sustain to the maximum. Select global and turn source 2 off.

Select source A again to see the sample. Now hold a note and you will hear the entire sample play back. It's a rhythmic loop!  Then turn the arpeggiator back on and hold a note. You can see how the start of playback of the sample is always different.

Then turn the effects back on and hold one note. The delay effect is syncopated (one channel 1/8 note, the other dotted 1/8 note) and the modulation effect is not tempo synched. What you hear is to the ear pretty random.  Play a chord, and it gets ever more random sounding.

Now set the AHSDR 2 sustain back to 0 and play a chord. It sounds percussive again, but even with a single note held, it still sounds pretty random.

So the notes played are the same every time but the sound coming out of Alchemy is not the same every time. Hope this helps explain what is going on here.

Thank you Enossified, 

I'll try to fix this the way you explained and most probably questions will arise and I'll get back to you if you don't mind :). Thanks again! 

[Anne22]

21 hours ago, scg said:

Maybe enossified covered this and I missed it, but there's also some random sample-and-hold modulation in that preset (which affects, among other things, the sample start parameter). You'll probably find similar random modulation in other sounds that behave similarly. I'm not aware of a way to make that deterministic. If you wanted to really dive into the sound design, you could possibly replace the sample-and-hold modulation with a sequencer modulator or perhaps external automation, although making that change might not be entirely trivial...

A more prosaic solution would be to bounce it out until you get something you like, and then use that (although that would have its own disadvantages).

Thank you Scg, 

You guys write a scientifically complicated text 🙂 and it will take me some time to digest it. As for bouncing , I was thinking about that, and even tried this little bit and it seems you may wait forever to get something you like. I get pissed off when I hear a fantastic arp playback which then disappears. Anyway, I hope we'll find a solution to that. Thanks. 

[David Nahmani]

The problem with these kinds of sounds is that by the time you remove the random aspects, they may no longer sound the way you liked in the original patch. So bouncing as audio may be a solution if that kind work for you. 

To dissect the sound in question, you can notice that it's made of two sources, A and B, that are mixed together. Each source has its own amount of random modulation. 

First, let's isolate source A: 

1. In the sources, click "B" to disable it: 
   
   
    
2. Now in the column on the left, click "A" to see the detailed parameters for source A: 
   
   
   
   If you play a note, you'll see on the waveform that it keeps starting in different places in the waveform, that's because the "Start" point is randomized: 
    
3. Click the "Start" knob to access its modulation sources: 
   
   
    
4. In the MODULATION section, turn off the first modulation:
   
   
   
   Now you can adjust the "Start" knob to start the waveform where you want, only it will keep repeating always from the same spot from now on, so you no longer get the same sound. Instead, you could turn that first modulation back on and choose another source (that is not random) to modulate the start position.

Hope that helped at least understand the process, even though I tackled only source A, the idea is the same to figure out what randomizes a modulation in source B.

[scg]

3 minutes ago, Anne22 said:

Thank you Scg, 

You guys write a scientifically complicated text 🙂 and it will take me some time to digest it. As for bouncing , I was thinking about that, and even tried this little bit and it seems you may wait forever to get something you like. I get pissed off when I hear a fantastic arp playback which then disappears. Anyway, I hope we'll find a solution to that. Thanks. 

Yes, this is an issue with randomization, and you're not the first one to notice it 🙂 Sometimes true randomness is what one wants, but other times, what you really want is something that's randomly generated once, and then remains exactly the same after that. To use some more scientific language, what would be nice would be a customizable seed value for the random number generator, but that doesn't seem to be a common feature.

There are many other techniques you can use to generate reproducible random content, but I don't want to give you more information than you're looking for at the moment. Instead, I'll just mention a couple features that might be of interest to you, such as the 'record MIDI plugin output' feature, and the various one-time randomization features in the MIDI editor.

[Anne22]

On 3/21/2023 at 10:26 AM, David Nahmani said:

The problem with these kinds of sounds is that by the time you remove the random aspects, they may no longer sound the way you liked in the original patch. So bouncing as audio may be a solution if that kind work for you. 

To dissect the sound in question, you can notice that it's made of two sources, A and B, that are mixed together. Each source has its own amount of random modulation. 

First, let's isolate source A: 

1. In the sources, click "B" to disable it: 
   
   
    
2. Now in the column on the left, click "A" to see the detailed parameters for source A: 
   
   
   
   If you play a note, you'll see on the waveform that it keeps starting in different places in the waveform, that's because the "Start" point is randomized: 
    
3. Click the "Start" knob to access its modulation sources: 
   
   
    
4. In the MODULATION section, turn off the first modulation:
   
   
   
   Now you can adjust the "Start" knob to start the waveform where you want, only it will keep repeating always from the same spot from now on, so you no longer get the same sound. Instead, you could turn that first modulation back on and choose another source (that is not random) to modulate the start position.

Hope that helped at least understand the process, even though I tackled only source A, the idea is the same to figure out what randomizes a modulation in source B.

Hi David. I think I have found the solution. Of course, I will go through all this what you said. You know what I think now? Randomization is an AWESOME feature. While bouncing repeatedly I got not only the version I wanted, but also other different versions which I DID like, which I didn't notice before.  Now I can use a few terrific sound versions in different sections of the same track. This makes my project much more interesting. Thank you all guys. Let's keep in touch!

[David Nahmani]

13 hours ago, Anne22 said:

Thank you all guys. Let's keep in touch!

You're welcome! And great, that's really good to hear that you were able to find a way to make a creative use of the results you were getting. Happy accidents are a huge part of the creative process IMO. The talent sometimes comes not in the shape of having complete control over the technology and use it to convey an idea originally born in your mind, but in the shape of making mistakes, hearing them and having the open mind to hear the result and enjoying it and finding a creative way to use it in your productions. I've done that many times myself. 😄