Mic-in real-time granular synthesis in Pure Data

As with the offline granulator that we’ve discussed in the previous post, finding resources for real-time granular synthesis on PD was for me even harder. As far as I could figure out, the simple approach that is presented here has not been previously discussed, but I think that this approach is the most efficient, lightweight and intuitive. So please have a look at this post and the example patch and I’ll be very happy to receive any comments, suggestions, questions etc…

Goal: we want to have a look at the intuition behind making a patch that allows basic granular synthesis in real-time on the mic-in signal, using some tools that Pure Data offers. Basic granular synthesis in the context of this post includes the following parameters:

  1. Grain starting time: how far back in the mic input will the grains be collected.

  2. Grain length: how long the grains will be.

  3. Playback speed: how quickly will the grain be played, affecting the pitch of the grain as well.

The example patch given in this tutorial is a bit more “dirty” than the patch parts that are shown in the text illustrations because there are some complicated relations that need to be taken care of; those relations are beyond the intuitive purposes of this tutorial, so the interested reader is referred to the example patch, which automatically adjusts the aforementioned plus some additional parameters, e.g. grain panning, volume, option for octave-locking and grain firing rate. By abstracting this patch, bigger patches can be made that allow more impressive results on real-time granular synthesis.

Real-time? Circular buffer! 

A circular buffer or a ring buffer, can be imagined as a round tape that has a recording head, say on top, and while it is turning, new audio is recorded over old audio. How far back will audio start being recorded over is a matter of the tape length. The circular buffer that comes built in with PD is the [delwrite~ ] object. Figure 1 shows a graphical example of a circular buffer and the PD implementation, considering that the tape has a length of 5 seconds.


Figure 1: The circular buffer (ideal for real-time mic-in processing) and it’s implementation in PD.

Play something on this circular buffer.

To make some sound out of this circular buffer, we need to place a play head, implemented with the [vd~ ] object in PD, at some position of this buffer. The delay time (given as a signal in the [vd~ ] object) defines the how far back we need to take sound from – later on this will be the grain starting time. Figure 2 shows the illustration and the PD implementation of a 300ms delay time.


Figure 2: Playing some audio from the circular buffer/tape.

Isolate a (short) part.

Until now we are able to go back in time in the mic input and start playing continuously what we has been played a while ago (300ms in our example). Figure 3 shows how we can actually trigger an amplitude curve that allows only a short part of what was going on 300ms ago to be heard. The volume envelope comprises a cosine function driven by a [line~ ] object and the time of the line object defines how long the audible segment will be – in this example the time segment is 100ms. Shorter segments are probably more usual in granular synthesis, but let’s consider 100ms for this tutorial.


Figure 3: Isolated short part from the tape.

Pitch up (faster) / pitch down (slower).

If we start moving the playhead on the tape, then the pitch of the recorded material will be affected.

  • If we move it closer to the recording head, then the playhead plays the tape’s content faster and therefore we have pitch-up.

  • If we move it away from the recording head, then the playhead plays the tape’s content slower and therefore we have pitch-down.

The illustration on the right in Figure 4 shows both directions, but the PD patch part on the left shows only the slower case. For playing the tape’s content slower we need to gradually move the playhead away from the recording head (increase the delay time in the [vd~ ] object). This is done by the [line~ ] object that substituted the [sig~ ] object on top of the [vd~ ] object. In this example, during the 100ms that the audible segment “survives”, the playhead moves from 300ms (direct initialisation of the [line~ ] object) to 400ms.


Figure 4: Pitch up/down (only pitch down is shown in the PD patch on the left)

That’s a grain!

As Figure 5 indicates, this patch part is what we need to control the three aforementioned parameters (grain starting time, length and playback speed); thus we have a basic implementation of a grain.

  1. Grain starting time is controlled by the parameter value in the green box.

  2. Grain length is controlled by the parameter value in the red boxes.

  3. Grain pitch is controlled by the parameter value in the bleu box (greater value than the one in green box causes pitch down and the vice versa).


Figure 5: That’s a grain!

A simple patch built by a online single grain from mic-in and randomness

The example patch given allows monophonic granular synthesis on mic input with setting some random parameters. This patch implements the ideas of granular synthesis discussed until Figure 5, along with some additional parameters, includes controls for setting the minimum and the range of random variation for the following parameters:

  • Firing rate (how often new grains are fired).

  • Grain starting time.

  • Grain length.

  • Grain speed-pitch.

  • Grain starting volume.

  • Grain panning.

Initially, maximum grain length and maximum delay time are set and almost all horizontal sliders are giving relative percentages based on those maximum values. There are many interrelations between the different parameters in order to avoid glitches and other things that can go wrong. E.g. it is not possible to have the play head 50ms away from the rec head and request (for pitch-up purposes) to move the playhead 100ms towards the rec head since this way the playhead will have to go 50ms in the… future!

I’m also preparing a bigger patch that includes combined abstractions of single grains based on this tutorial patch. I’ll make a new post about bigger patches for both file-based and mic-in-based granulators. Stay tuned!


Granular synthesis on audio file with Pure data

Finding resources about how to make a proper patch for granular synthesis on PD was for me a lot harder than I expected. So I’m sharing what I’ve found and what I’ve figured out by myself in hope that others will save lots of their time when trying to approach granular synthesis with PD.

The patch of this tutorial can be found here and a video that explains what this patch does can be found here.

Goal: what we want to build, is a simple instructional patch that loads a wav file and at random times it takes a single grain (with random parameters) out of the loaded file and plays it. The controllable parameters of the patch will be the following:

  1. Grain density: how many grains per second we expect to listen.

  2. Grain starting time: position of the loaded file that the grain starts.

  3. Grain length: how long the grains will be.

  4. Playback speed: how quickly will the grain be played, affecting the pitch of the grain as well.

Additional parameters could be set, e.g. grain panning or volume, but for the sake of this tutorial we’ll stick to these four.

Basics: We consider a grain to be a (usually very short) segment of an audio file, the amplitude of which is regulated by an envelope. The playback speed of a grain can vary, along with other things that are not considered in this tutorial. Figure 1 shows an audio segment on the left, the envelope on the right an the resulting waveform that is obtained by applying the envelope the audio segment.

In Figure 1 the length of everything is fixed to 100 ms. Additionally, the audio segment does not come from a file but from an [osc~ 100] object.



Figure 1: Granular synthesis basics.

Load a file, take a segment and apply envelope.

As a first step, what we need to be able to do is:

  • Load an audio file.

  • Select a starting and an ending point on this file, according to the grain length.

  • Modify the length of the envelope so that it fits that of the segment.

– Load an audio file.

Loading a file is performed in the part of the patch illustrated in Figure 2. Please notice that the patch will need to know later on what the size of the file is ([s fileSize]), and the maximum length that we consider for grains ([s maxLength]). Additionally, notice that the starting index horizontal slider (as any other slider in the patch) are in [0, 1], making all values in the patch relative to the desired/selected file size and maximum grain length.


Figure 2: Loading an audio file to take grains from.


– Select a starting and an ending point on this file, according to the grain length.

A suitable object to do it is the [line~ ] object, that will allow us to read from any index to any index of the of audio_file, in any amount of milliseconds we desire. Figure 3 shows a part of a patch where we can select a starting index (left), length (middle), playback time (right) and play it by hitting bang on top. Notice that for setting starting index and length into the [line~ ] object we use an intermediate [f ] object for suppressing the bang while changing these value, since these bangs activate [line~ ] and cause glitches while values in this number boxes are changed. Notice also that priority of bangs is very important when we need to finally play the grain: first we have to set [line~ ] to the starting index directly, second we need to make sure that the desired time duration is indeed as a second value in the list and third set the first list value, activating the [line~ ] object and playing the file.


Figure 3: Selecting starting and ending points on the file.

 Modify the length of the envelope so that it fits that of the segment.

Figure 4 shows the integration of an envelope on the right side of the patch part of Figure 3. The envelope is the same as the one illustrated on the right side of Figure 1, but the one in Figure 4 receives a variable time length from the number box that also sets the grain duration time. Notice that priority of setting the envelope values and triggering it is also important. Specifically, first, the envelope [line~ ] is set to 0; then, time is set along with setting the time in the segment’s [line~ ] object; finally, the [line~ ] in the envelope part is instructed to go to 1 within the given time interval directly when the [line~ ] of the segment is activated (by the list that arrives from the [pack 0 0] object on the left).


Figure 4: Modifying the envelope length.

A simple patch built by a single grain and randomness

The example patch that implements the idea of granular synthesis discussed so far is illustrated in Figure 5, along with some annotations that clarify some of the patch parts that haven’t been explained above. The following should be noted:

  • There are horizontal sliders that control the starting index, grain length and speed (as well as an additional slider below the waveform of the loaded array to indicate the part of the file that the grain is taken from).

  • There is an automation part in the bottom-right part where all these parameters are controlled, plus a metro that activates the current grain (at random time intervals).

  • There is a tricky bit in the box that includes the [min ] object: there is a chance that the grain size is larger than the metro firing rate, e.g. if the grain length is 100 ms and the next grain comes in 50 ms (according to metro time), then a glitch is going to happen. To avoid such glitches, we take a grain length the minimum of the slider-selected grain length and the current metro firing rate.


Figure 5: The complete example patch and some explanatory indications.

Feel free to ask, comment or propose anything! I’m planning to make another tutorial patch on real-time granulation of microphone input using Pure Data’s circular buffer: the [delwrite~ ] object. Additionally, I’m planning to make available two heavy-duty PD patches I’m preparing, that take advantage of (too) many grains and additional controls for file-based and real-time granular synthesis. Stay tuned!

Echo Pitch for iPhone is here!

Avi Bortnick and myself have been designing and developing an app that’s hopefully going to inspire a lot of people who make music using iPhones.

Echo Pitch – a pitch-shifting multi-delay that has 4 synced delays where each delayed signal can be pitched one octave up or down in 1/2 steps. Echo Pitch also has a built-in simple looper, amp simulator, master delay, reverb and can function as a 4-voice harmonizer. Each of the four delays can be routed into the other for incredible, swirling, ambient washes and otherworldly sounds. You really need an interface – like iRig, Fender Slide, Apogge Jam, etc, to use it, or at least headphones. Otherwise, you’ll get gnarly feedback. 

iTunes link is here, while a demo video by Avi Bortnick is below:



Stay tuned for updates 🙂