He has connected the iPad’s 1/8” Stereo mini headphone output to the MODX A/D Input using an appropriate adapter to deliver the signal.

(stereo 1/8” mini male to two 1/4” mono male phone plugs).

Normal configuration (connecting via TO HOST direct to iPad/iPhone) you would not have to include this cable/adapter to the A/D Input — meaning: you could connect just via USB and the app would return audio via the digital connection direct to the MODX main outs, but you would not be able to manipulate the app’s audio further within the Motion Control Synthesis Engine...

Delivering the iPad/iPhone’s analog audio Out to the MODX via the A/D Input allows you to control that input from the iPad/iPhone as an external audio source, which means you can treat it as one controllable sources. You can use it to Side Chain, you can use it to set Tempo, etc., etc., etc.,

Please note - newer iPads/iPhones may not include the dedicated headphone output. Like me, the video guy has an older iPad (you can tell it still has a dedicated headphone jack) ...whoever thought eliminating the Phones Jack was a good idea was not a musician.

If you have a newer iPad/iPhone with no dedicated phones jack I guess there is (yet another) Adapter you can get from Apple... that gives you a standard mini headphone jack in addition to the regular (power) connection.

Side Chain Possibilities
Several of the Effect Types allow external input which means the audio signal can be used to influence the behavior of that processor. And as the video shows incoming tempo can be derived from external audio... as you can see, this opens up to a world of possibilities for real-time interaction.

Please see the following for an introduction to the Side Chaining possibilities:
Mastering MODX: Side Chain Modulation
Mastering MODX: The Envelope Follower

Thanks for this Bad Mister,

But honestly I can't get this to work. So I have everything connected the Yahama and the Iphone with Synth book app, I use the A/d input and I have a drum playing from the Apple comming in through my synth and the speaker, but still I cannot figure it out. I have set part 1 and part 2 like in the explaination Mastering Modx: the envelope follower, but nothing happens.
In the video Luke Juby controls sounds with the app coming in from the Yamaha. How do I set up the Yamaha to do the same as Luke Juby? Can you explain to me how I need to set up the controls to have the Envelope to work like in the video I share?
Part 1?
Part 2?

I like to do the same as Luke Juby does in the video, I have read the manuals you have shared previously, but still I don't find how to set up the synth
Can you give me a step by step?

The picture shows "EnvFollow 2" as the source controller. If you click on the "Edit Envelope Follower" button, you'll see the meter bars are not "dancing around" in response to the iPhone audio input. "EnvFollow 2" means PART 2 is being listened to in order to convert PART 2's level to a value 0-127. "EnvFollow 5" would be listening to PART 5. You need to listen to the A/D input. EnvFollowAD would follow the A/D input where your iPhone is supplying the sound.

Once you have audio routed properly to the A/D IN (the peak light should only flash intermittently— steady red is bad), you can route that audio into the Motion Control Synthesis Engine. We can take a look at Side Chain Compression and Envelope Follower.

Side Chain Compression is where the incoming audio (he used a “4-on-the-floor“ Kick drum) causes the synth pad sound to “duck” (dip in volume) each time the drum hits. When he turns down the input the synth pad sound is steady. This is a familiar thing in dance/house music...

Call up a Single Part Performance. It is best to begin your experiments on a Single Part. Then when you are familiar with how it works expand to other programming. A Single Part Pad or String sound will be fine — any sound that sustains.
From the HOME screen
Touch the “Type/Name” box 1 to see the pop-in menu
Touch “Edit”
Touch “Effect” > “Routing” > here you want follow the routing of the active Elements or Carrier to the Insertion Effects block.
Set one of the Insertion Effect to a “Compressor VCM 376” which features a Side Chain Input.

In the diagram Insertion A and Insertion B each have an On/Off and can be set by tapping on the box with the name... select “Comp” > Compressor VCM 376
Just above, set the Side Chain = A/D
By selecting A/D audio will be passing through Part 1 via this Insertion Effect.

Touch “InsA” or “InsB” whichever you used, and view the parameters of this processor.
Input Level, Ratio, Attack Time, Release Time, Output Level, Side Chain Level

In general you set this according to your source material. We can tell you a Kick drum has a very quick Attack Time - so the lower the number the better. If you set this too high it will not respond to the strike. Release Time influences how long it is before the compressor will be able to engage for a new Attack. If you set this too high it will not reset fast enough for the next drum strike. These two time based settings are critical. A Kick drum can come and go in less than 200ms

Work with them and you’ll see just how critical it is to dial these in just right.

Envelope Follower allows incoming audio to influence the internal synth sound. In this case the incoming audio creates a pulse or shape that you can apply to an internal parameter. For example, assigned to Volume it could be set to do the opposite of the Side Chain Compressor... instead of ducking (turning down) the synth sound, we can have that Kick drum pulse cause the sting/pad sound increase in volume - following the shape created by the kick drum pulse.

Again work with a Single Part string or pad (sustaining)
From the Home screen
Touch the “Type/Name” box 1 to see the pop-in menu
Tap “Edit”
Touch “Effect” > “Routing” > on the right side of the screen tap the box that says “Envelope Follower”

Set the dialog box so “A/D“ is feeding into the Envelope Follower
Along the bottom of the screen you will see A/D has an arrow pointing up (feeding the Env Follower)
The top meter is the incoming signal. Set the Attack and Release... understanding kick drum is quick and Release should not be too long (it needs to reset.
The bottom meter is the controlling envelope output.

Next to the slot that is the A/D is your single Part 1 and the word Edit below it, tap “Edit”
This is a shortcut to the Part 1 Edit Control Assign screen

Here “EnvFollowAD” is ready to be assigned...
Touch the “+” to add a Destination (parameter)
When the default parameters appears... tap it to see the pop-in menu

Select “Part Parameters” > “Volume”
On the Control Assign screen set the “Polarity” to Bi this will allow the sound to pulse louder with each kick drum hit.
“Ratio” will control how much

As you can see you can route this to any number of Destinations - try Pitch, experiment.

The video also (actually) shows you how to setup the Clock sync to A/D IN.
Using the Remixer with the MODX will give you tons and tons of possibilities.

The results you get, quite naturally, depend a lot on the source material. The busier the audio the less distinctive it is, you are looking for audio contour you are looking for “shape” the audio causes.

Dear people I appreciate this help, but after all this it still DOESN'T work

I don't know what I am doing wrong, I do everything said above and explained. The sound coming in from the Iphone doesn't stop or kick in when I press my keys???

I have the device connected and I play a drum on the Iphone, I hear the drum perfectly through the speaker when I press in the App Yamaha synth on the pink square representing a drum. And the drum continues playing;so the only thing that stops the noise is turning down the volume. Normally you would press the square on the app, and the drum is kicking in after a key is hit, right or not, Well like last time none of the things I tried or any of your explainations work, I litteraly tried different options like the Envelope to part 2. What is the problem??

I really have no idea...

The device that connects the Iphone is just a new adapter allowing to put in a stereo jack thus transforming to 2 big jack that go in the audio IN L/R and the sound is that commes in is perfect
But after all this, and I did everything to the letter, I can't seems to do the work. A drum, or synth noise from the Iphone is even affected. In the video with Luke Juby you see him turn the tempo up and down and even a delay and a break in the melody, but I don't have any of that. The only thing I can affect is the sound comming from the Iphone, but sound from my Yamaha synth do go to the Iphone.

I noticed when I go to evenlope follower, the arrows are correct when I play the drum comming from the Iphone the master, volume bar is also showing movement, I don't know if this is correct.

Is there anything else?? Do I need to do something to the "Audio in" in the Edit menu, Something else maybe, I checked the connections and they say 2 times Main L&r output is this OK? I have added a picture

OOOpppps so sorry for the incovience I took a look at the output and yes this was the problem all the TIME, The output must be turn of or the music from the Iphone is just playing,

Thanks so much for everything, sorry for any loss of time. Changing the output.. who ever thought....

Thanks so much Jason and Bad Mister

Excellent...