Tuesday, 26 March 2013

The patch

Now that the electronics are operational, the bike built and running, the parts assembled, it comes the time to shape the sound as desired.

I've decided to separate the different pads to different sounds. The drum pads are going to be bass drum and snare, the left button pad should trigger some kind of fat filling ambient bass sounds, the right button pad will be linked to keyboard chords.

These sounds will be rendered from Logic Pro. The PD patch will take the inputs from the bike, turn them into midi signal and send it to Logic. Logic will get the midi in different channels. Each channel will be a software instrument. The specificity of each instrument will be preset to the project. There will be, however, variables to each one. These variables are taken care of via a Lemur patch. Moreover, the variables are not only for the sounds in Logic but as well the signal reception in PD.

Another aspect not yet approached is the sensors and how they will affect the sound. So far, the only affectation roughly made comes from the crank cadence, received via the hall effect switch. Two things were made: an RPM counter with an added 2x multiplier. This will meet more likely the BPM of the listened sound. The reason is that the effort in cycling with equivalence between BPM and RPM is not likely. As a cyclist who listens to music while commuting, I don't find it feasible. On the other hand, BPM=RPM*2 is a common practice. This way every time and foot pushes the pedal equals a beat. This will have several sound affectations and probably other multipliers. However, the only connection I've made so far is to a delay effect on the drum section.

As to the other two hall effect sensors the maths are different and so will be the way they'll affect sounds and the sounds they'll affect. First of, the maths. These sensors don't output signal from 0 to 1 but rather from roughly 0.5 to 1 or 0.5 to 0 depending on the magnet pole approaching it. However the to value also depends on the strength of the magnet. Due to size matters the magnets used only take the value to about 0.85. Therefore, the range of +-0.5/+-0.85 which is about 0.35 will have to be multiplied to meet the range 0/127 equivalent to midi values. Also, due to circuit stabilising, the negative output (0.5/0) is seriously damped, therefore the usage of the positive values. An important note is that once the sensor and corresponding magnet are on the brake levers, meaning that their standby position provides the maximum value and decreases upon usage of the brakes. So, in terms of midi values, it will start at 127 down to 0 rather than the opposite. There is the possibility of creating an equation to invert this, however, the first attempts are going to meet what the sensors provide.

 

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