Author: Tom Zicarelli

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ep-413 DSP week 6

Convolution and Voices

 

Convolution

part 1 – The time domain:

(The frequency domain):

The impulse response

  • Decomposition
  • Unit impulse (delta function)
  • convolution (from the input side and output side)
  • filters

From the output side:

Screen Shot 2014-10-05 at 3.01.04 PM

The convolution sum:

Reference: http://www.dspguide.com “The Scientist and Engineer’s Guide to DSP”, By Steven Smith – chapters 6-7
Common impulse responses:
F_7_1.gif

A ‘block diagram’ of a high pass filter. The impulse response of  low pass filter is subtracted from the impulse response of an all pass filter. Note that the all pass filter is the ‘delta response’:

Applications

Voices

Examples

Questions

 

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ep-413 DSP week 5

Assignment:

Composition: Sound-byte 

  • The sound-byte is a short audio clip of speech.
  • The speech can come from anywhere. Something familiar, something famous, something unusual.
  • Every sound in the composition is derived only from the sound-byte. You can use any tool or method.
  • The sound-byte in its original form should occur somewhere in the piece
  • Duration: roughly 2-3 minutes?  That is up to you.
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Pitch tracking in Max

Two methods, In the time domain.

Counting zero crossings, in the time domain, to measure the period and frequency of a sine wave, using zerox~ and edge~

A patch by Mari Kimura that compares the Max fzero~ object with the IRCAM gbr.yin~ object – measuring frequency in the time domain. gbr.yin~ uses autocorrelation.

Note: gbr.yin~ is part of the FTM package. Download and install from here: http://ftm.ircam.fr/index.php/Download

download

https://github.com/tkzic/max-projects

folder: pitch-tracking

patches:

  • zerox-test.maxpat
  • MKtest-pitchtrack.maxpat

 

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ep-413 DSP – week 4

Notes:

Audio Signal Processing Course: https://www.coursera.org/course/audio

By Xavier Serra and Julius O. Smith

This is a free course offered by Stanford. It starts at the beginning of October. I will be taking the course and would be happy to help you if you are interested in taking it too.

Pd weekend 2014: Katja Vetter Microphone design: http://libguides.lib.siu.edu/puredata

Part I – Pitch detection

How would you construct an ‘Autotune’ effect that works in real time?  The first requirement is accurate pitch detection:

Frequency domain:

FFT and STFT: Find frequencies where the signal has greatest energy. Tradeoff between frequency and temporal resolution. Moderate latency.

Max examples: https://reactivemusic.net/?p=11202

Also look at the builtin Max tutorials on the fft~ and pfft~ objects

3rd party Max/Pd objects:

DSP code

Time domain:

Zero crossing: Measure the period of waves by counting rate of zero crossings. Doesn’t work with complex waveforms.

Max objects: fzero~ and zerox~

Autocorrelation: Compare a signal with a time shifted copy of itself.  Low latency but CPU intensive. Can be improved by using lower sample rates and other tweaks. (Helmholtz)

Example patches: https://reactivemusic.net/?p=17169

(note: gbr.yin~ is a 3rd party object from IRCAM, but is built into Max)

Pd examples from Katja Vetter: (helmholtz~ external)

We also looked at Katja’s new app: InstantDecomposer. If you would like to try this patch, please contact me. I will need to get permission from Katja.

Wavelet transform:
Other methods:
  • phase locked loop
  • human pitch matching (what is the latency?)
  • Neural networks?
  • Statistical methods (pattern matching)?

Part II – Prototyping

Muse development case study: https://reactivemusic.net/?p=16187

Assignment

Next week we will listen to your music from the future.

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ep-413 DSP – week 3

Composition tools

Make music using X

“Lyrebirds and Acoustic Guitar” by Chris Lopez

Tools used by students in this class:
  • Reverse engineering the style of a reference song. Use a Midi keyboard + Logic
  • Maschine + microphone
  • Modular synth + Midi
  • Listening to melodies in your head + Ableton Live
  • Building a chord progression, playing piano, guitar, Ableton Live racks
  • Composing with drums in Ableton Live. Building a form or structure. Using the ideas in your head.
  • Ableton Live.  And playing the guitar.
  • Finale music notation software.
Dramatic shape:

Every performance has a dramatic shape. That is, excitement level measured over time.

What is the shape of this piece:

References:
Notes:

Like stories, songs have beginnings, endings, and journeys that connect.  Many forms can be applied, but the goal is always the same – to have maximum impact on the listener – to communicate honestly with strength and conviction.

As you listen to music, be aware of the form – especially in terms of the dramatic shape.  Where is the peak of intensity?  Does the music grab your attention immediately, or does it build slowly?    How much repetition do you hear?  Can you find suspense, surprise, humor, sadness, power, or beauty?  What musical elements work together to create these feelings?

The most powerful tools you have as a composer are your ears.