A Partial SynthDef

A SynthDef for a single partial with amplitude and frequency as arguments. In addition, the output bus can be set. The sample rate is considered to avoid aliasing for high partial frequencies.

(
SynthDef(\spatial_additive,

      {
              |outbus = 16, freq=100, amp=1|

              // anti aliasing safety
              var gain = amp*(freq<(SampleRate.ir*0.5));

              var sine = gain*SinOsc.ar(freq);

              Out.ar(outbus, sine);

      }
).send;
)

The Partial Synths

Create an array with 40 partial Synths, using integer multiple frequencies of 100 Hz. Their amplitude decreases towards higher partials. An audio bus with 40 channels receives all partial signals separately. All synths are added to a dedicated group to ease control over the node order.

~partial_GROUP = Group(s);

~npart         = 40;

~partial_BUS   = Bus.audio(s,~npart);

(
~partials = Array.fill(40,
{ arg i;
  Synth(\spatial_additive, [\outbus,~partial_BUS.index+i, \freq, 100*(i+1),\amp, 1/(1+i*~npart*0.1)],~partial_GROUP)
});
)

s.scope(16,~partial_BUS.index);

The Encoder SynthDef

A simple encoder SynthDef with dynamic input bus and the control parameters azimuth and elevation.

~ambi_BUS      = Bus.audio(s,16);

(
SynthDef(\encoder,
      {
              |inbus=0, azim=0, elev=0|

              Out.ar(~ambi_BUS,HOAEncoder.ar(3,In.ar(inbus),azim,elev));
      }
).send;
)

The Encoder Synths

An array of 16 3rd order decoders is created in a dedicated encoder group. This group is added after the partial group to ensure the correct order of the synths. Each encoder synth receives a single partial from the partial bus. All 16 encoded signals are sent to a 16-channel audio bus.

~encoder_GROUP = Group(~partial_GROUP,addAction:'addAfter');

(
~encoders = Array.fill(~npart,
      {arg i;
              Synth(\encoder,[\inbus,~partial_BUS.index+i,\azim, i*0.1],~encoder_GROUP)
});
)

~ambi_BUS.scope

The Decoder Synth

A decoder is added after the encoder group and fed with the encoded Ambisonics signal. The binaural output is routed to outputs 0,1 - left and right.

// load binaural IRs for the decoder
HOABinaural.loadbinauralIRs(s);

(
~decoder = {
Out.ar(0, HOABinaural.ar(3, In.ar(~ambi_BUS.index, 16)));
}.play;
)


~decoder.moveAfter(~encoder_GROUP);

References

The German Pavilion

The German Pavilion at the 1970 Expo in Osaka was an elaborate spatial audio project. Various artists, including Bernd Alois Zimmermann, Boris Blacher and Karlheinz Stockhausen, contributed works for the spherical loudspeaker setup:

The German Pavilion at the 1970 Expo in Osaka.

A device for live spatialization in the Osaka Pavilion was developed at TU Berlin.

TU-designed 'Kugelsensor' for live spatialization in the auditorium.

Stockhausen

The following sketch shows Stockhausen's approach for working with the system, using an 8-track tape machine:

Sketch for Stockhausen's work 'Hinab-Hinauf'.

TU Composition

The WaveGuide Class

The WaveGuide class implements all necessary components for a waveguide string emulation. Inside the class, the actual waveguide-buffers are realized as pointers to double arrays.

From ``WaveGuide.h``:

/// length of the delay lines
int     l_delayLine;

/// leftward delay line
double  *dl_l;

/// rightward delay line
double  *dl_r;

The pointer arrays need to be initialized in the constructor of the WaveGuide class.

From ``WaveGuide.cpp``:

dl_l = new double[l_delayLine];
dl_r = new double[l_delayLine];

for (int i=0; i<l_delayLine-1; i++)
{
    dl_l[i] = 0.0;
    dl_r[i] = 0.0;
}

Plucking the String

The method void WaveGuide::excite(double pos, double shift) is called for plucking the string, respectively exciting it. It receives a plucking position and a shift parameter. In two loops, the method fills the two waveguides with the excitation function. In this example, a simple triangular function is chosen.

From ``WaveGuide.cpp``:

// set positive slope until plucking index
for (int i=0; i<idx; i++)
{
    dl_l[i] = 0.5* ((double) i / (double)(idx));
    dl_r[i] = 0.5* ((double) i / (double)(idx));
}
// set negative slope from plucking index to end
for (int i=idx; i<l_delayLine; i++)
{
    dl_l[i] = 0.5*(1.0 - ((double) i / (double) (l_delayLine-idx)));
    dl_r[i] = 0.5*(1.0 - ((double) i / (double) (l_delayLine-idx)));
}

Oscillating

White Tone Oscillator

As explained in the Sound Synthesis Introduction, the Karplus-Strong algorithm is based on a sequence of white noise. The following example uses a feedback structure to create a looped version of a white noise array:

Main components of the above example are the excitation and the resonator. The resonator is a feedback loop with an adjustable delay:

The excitation passes a random sequence to the resonator, once the gate is activated. It will oscillate until the gate is released.

Load the example in the Faust online IDE for a quick start:

// white_tone.dsp
//
// Henrik von Coler
// 2021-07-04

import("all.lib");

// Control parameters:
freq = hslider("freq Hz", 50, 20, 1000, 1) : si.smoo; // Hz
gate = button("gate");

// processing elements for excitation:
diffgtz(x) = (x-x') > 0;
decay(n,x) = x - (x>0)/n;
release(n) = + ~ decay(n);
trigger(n) = diffgtz : release(n) : > (0.0);

P = SR/freq;

// Resonator:
resonator = (+ : delay(4096, P) * gate) ~ _;

 // processing function:
process = noise : *(gate : trigger(P)): resonator <: _,_;

Karplus-Strong in Faust

The Karplus-Strong algorithm for plucked string sounds is explained in detail in the Sound Synthesis Introduction. That implementation is based on a ring buffer with a moving average filter. For the Faust implementation, this example has been adjusted, slightly (Smith, 2007).

References

Getting the JackTrip Source Code

Now the JackTrip source code can be downloaded from the official JackTrip repository.

git clone https://github.com/jacktrip/jacktrip.git
git checkout nils

Changes in the remote repository have to get pulled.

git pull

Afterwards you can follow the official build instructions.

Copying to a Remote Machine

The following command copies the file testfile.html from the local machine to the home directory of the user student on the server with the address specified address 11.22.33. Instead of the home directory (~/), any other target can be specified:

$ scp testfile.html student@11.22.33:~/

Add the -r flag to copy a directory recursively:

$ scp -r /foo/bar student@11.22.33:~/


.. admonition:: Exercise

  Select or create a short WAV file on your local machine and copy it to your personal directory on the server using SCP.

Copying From a Remote Machine

To copy a file from a remote server, the arguments' order needs to be swapped. The dot (.) copies the data to the recent directory. Any other path can be used as target.

$ scp student@85.214.78.6:~/WebAudioFreqGain.html .