Today I’d like to talk about the Techtar’s Ampmod sound module which does
what I call “pitch dependent polyphonic amplitude modulation”.
I demonstrate it in this video:
Amplitude modulation (am) means to change the volume of a signal over time.
The famous tremolo-effect, often used by guitarists, is based on am.
The ampmod module has two properties that I would like to point out:
First, it is polyphonic. That means the am effect applies to every string
separately so that every string can be modulated in a different way.
Second, the am-frequency with which each string is amp-modulated depends on
the strings current pitch.
The rotary encoders are used to change the following parameters. The
values for each string are represented by a dot on the 8*8 Led-matrix
and can also be edited separately.
middle position: no effect is applied.
left: full intensity unipolar am (amp-factor between 0, 1)
right:full intensity bipolar am (amp-factor between -1-1 (ring modulation))
2) frequency offset:
change am-frequency offset e.g. to apply detune-effect.
3) frequency offset range
change the range of the frequency offset parameter
am-freq offset in octaves
5) wave shape
morph modulation wave between sinus and pulse
change the response time of the am-frequency changes.
As you can hear in the video, there is quite a variety of different sounds
that can be made just by using this one sound module. When tuned to low frequency,
it produces a complex polyphonic tremolo sound. Tuned higher, into the audible
frequency range, the am isn’t perceived as modulation of volume any more,
but as modulation of timbre and pitch. If tuned one octave below the base
frequency of the string, it produces a rather authentic bass sound. When the
am frequency is odd in the relation to the string, some very dissonant
sounds can be produced, especially if bipolar am is used. Slowing down the
inertia brings funny transitions from one pitch to another. Last thing I
show in the video is to control the octave offset parameter by a
foot pedal on the ground-control (which I’ll show in another post).
All in all I’m very happy to get such a variety of sounds with such a simple
concept like amplitude modulation. This is very encouraging.
To give you a better Idea which components the Techtar consists of and how
they work together, I’ve made this flow chart down below.
If you have questions or feedback, please leave a comment. This is the best guide for me to explain the Techtar better and in a more understandable way.
Also I would love to discuss the musical and technical aspects with other musicians and makers to make it better and maybe build an open hardware community
project out of it.