Excitation (audio signal) in USB host mode

is it possible to get the excitation signal (I mean direct signal from the mic from back connector) even if the usb cable is still connected to a MIDI host?

I am thinking of using an external synth (an Axoloti) for using both MIDI data and excitation (in analog mode). Would that be possible without frying the input? (Axoloti has line level inputs)


That works. You could also patch the dry signal through to the sound card. Is that an option? Some latency will be added compared to CV mode, but it should still be quite OK.

I am afraid Axoloti cannot sync with the digital audio input or become a slave of this signal. It can only get analog audio.

My question then changes to how to create embedded audio synths for Tickle. USB MIDI is not a problem usually, but the audio part it is. We will need at least a raspi or similar computer. It would be great with Axoloti or OWL or similar… any plan?

We are working on embedded audio synthesis along with multi-touch, pressure sensing and polyphony. But it will be a completely different device! :slight_smile:

We just tested it. In USB host mode, you do get the analog excitation audio out on the back. Please check!


  1. USB HOST MODE with Axoloti works perfect! In seconds I could control a synth with the MIDI input coming from Tickle. Just connecting USB out of the tickle to Axoloti USB input Yeah, this is promising!

  2. Audio out from excitation: I have to admit that I tested it with a mono minijack connected to my mixer (using a stereo jack to minijack adapter) that is what I have now in my home studio. Tomorrow I will go to the uni and get a mono cable even if I have to deal with the virus haha.

If I connect it to Axoloti, what I hear is the sum of three sounds:

  1. a different tone for each of the hexagons
  2. the sound from the piezo
  3. a carrier in the background (see photo).

This is only the carrier without touching the Tickle:

If I connect it to my Laptop, I hear:

  1. the sound from the piezo
  2. the same carrier

If I connect the USB to a charger to Tickle (no USB host) I hear:

  1. the sound of the piezo
  2. some interference in the background but acceptable

Is this what is expected, or an issue with impedance, or an issue with the cable?


Hi Enrique,

When the tickle is not connected to a USB Host, it launches into analog mode. In analog mode, there is a frequency shifter applied to the piezo signal. You can control the shift frequency with the “timbre” knob. So when you turn the timbre knob, can you see the carrier signal changing? That might indicate, that the analog mode is activated. Only when the tickle sees the USB Host on startup, it boots in to the USB Host mode. You might also want to check, if your USB cable has a proper connection, when it looses the connection it might boot into analog while connected to the Axolotti. The different tones per hexagon also indicate a special analog mode where the frequency shift amount follows the pitch of the hexagons.


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Hi Clemens and Max,
the background sound (a loud carrier with a lot of harmonics as you see in the previous picture) definitely is present in USB Host Mode. I confirm Tickle is in this mode because I receive MIDI notes and CC in Axoloti, because no change in freq is produced while turning the timbre knob and because Tickle initializes in the way it always does when connected to my laptop. The sound of the piezo is also in the output, but the SNR is something like 6dB.

I also used a ground loop isolator (https://www.amazon.com/AUKEY-Ground-Isolator-Systems-Included/dp/B01L1NP7YI) between tickle audio excitation out and axoloti in, with a mono cable, and the sound persists. I guess it is some funny effect of adding your hardware in serial to another one (it happens the same with Axoloti or with a normal audio mixer)

Do you also have this background sound in your Tickle or is it only mine?

It is totally ok, I am trying to explore this excitation signal as it would be cool and easy to use for making synths with external gear like Axoloti or OWL. Maybe this is a feature you could offer in the future: an output with the piezo dry signal.

best and thanks

A test you could make is to just use a laptop on battery and only the Tickle connected to it. Is there the same noise then? (via USB, and possibly also on the analog excitation out.)

in regard to excitation signal, there is no difference in the background sound if tickle is connected to a laptop on battery only or charging.

However it is not so loud as when I connect it to the Axoloti or to an audio mixer. So the axoloti should not be the problem in this case.

It is not a hiss or a noise, it is a sound with a carrier and a lot of harmonics, as you see in the previous picture.

Finally, the digital audio signal in Pure Data is clean. I guess then it is something with the analog conversion in the excitation signal.

We just tried to hook up Spectroid to the Tickle while in USB host mode but Android doesn’t take the audio signal from the connected cable, even with the appropriate adapters. How did you do it?

It was just a quick check, no cables involved in this case.

I connected the excitation signal to my audio mixer and I simply sent it to speakers. I put my phone just in front of my speaker cone at 20 cm. No other sounds in my studio but obviously many other filtering effects (mic response, speaker response, room response, etc). But anyway the signal is not flat at all, actually it sounds like a 7th minor chord hahaha

Ah, so that could be a ground loop because the computer is connected to the mixer through the audio. I was trying to rule this out by connecting it directly into the phone.

When you heard that noise on the analog out jack, have the LEDs been on in that case? I know the LEDs can cause trouble, when at bright levels in combination with a not-so-nicely-filtered power supply.