# digital signal processing

"signals processed in this manner are a sequence of numbers that represent samples of a continuous variable in a domain such as time, space, or frequency"

notes about what i found important knowledge for sound creation

# links
* online book: [the scientist and engineer's guide to digital signal processing](http://www.dspguide.com/pdfbook.htm)
* book: The Computer Music Tutorial by Curtis Roads (1256 pages)
* online book: [spectral audio signal processing](https://www.dsprelated.com/freebooks/sasp/) by julius o. smith iii
* [sound texture perception via statistics of the auditory periphery: evidence from sound synthesis](https://www.semanticscholar.org/paper/Sound-Texture-Perception-via-Statistics-of-the-from-McDermott-Simoncelli/1c6ac9844de18855f51e13437c84e869590e4b1e). synthesis of sound textures
* [puredata](http://puredata.info/) graphical dsp programming. easy to create graphical interfaces with controls, for example when linking multiple midi devices

# subtopics
* [analysis and resynthesis](sound/resynthesis.html)
* [convolution](convolution.html)
* [frequency filtering](sound/filters.html)
* [notes](sound/notes.html)
* [phase generation](sound/phase-generation.html)
* [tools used by sph](sound/sph.html)
* [software implementation](sound/implementation.html)
* [synthesis](sound/synthesis.html)

# digital sound representation
a common format for storing signals digitally is sample values of the distance magnitude of a vibration over time, like positions of a membrane between two bounding values

## sampling rate
* also called sample rate
* describes how many samples represent one second of sound
* with a higher sampling rate, more and higher frequencies can be represented
* the maximum representable frequency in hertz is half the sampling rate, as any higher frequency than that would be spaced in a smaller duration than two subsequent sample values

# algorithms
* stateless: have only parameter values that need not be kept
* stateful: have parameters for values that need to be kept between function calls. for example, carryover values that fall outside the currently processed range and are used in the next one
* processing one input sample at a time: can affect multiple samples only with state and delay after accumulating samples
* segment to segment: processors might depend on preceding or following values
* one to many: output creates a longer signal
* many to one: a longer signal becomes a shorter one

# digital music making tools
* analog hardware devices for synthesizers with keyboards or sequencing
* software sequencers where instruments, synthesizer sounds, recordings and effects can be layed out and played back
* software environments like fruity loops, reaktor, reason and others
* lv2 or vst plugins as effects and synthesizers
* taking audio recordings and prepare their ordered playback in a program like ardour or cubase
* connecting hardware devices with midi and puredata and the user interfaces that it can create
* preparing sample arrays using a general purpose programming language and writing to sound files

# other
* [harmonic](https://en.wikipedia.org/wiki/Harmonic): a harmonic is a wave with a frequency that is a positive integer multiple of the frequency of the original wave
* [time series](https://en.wikipedia.org/wiki/Time_series): a series of data points indexed (or listed or graphed) in time order. most commonly, a time series is a sequence taken at successive equally spaced points in time
* a sound program is a potential for sounds to occur. elements can appear and disappear like entering and exiting a dimension. there is always some kind of seed, for example the literal arguments in program code
* amplitude: the magnitude of the difference between a variables extreme values. the amplitude of a periodic variable is a measure of its change over a single period
* clipping: limiting values to a maximum
* digital image processing is a subcategory of digital signal processing
* envelope: a path of loudness transition
* every linear time-invariant system can be represented by a convolution
* frequency: number of occurrences of a repeating event per unit time
* low frequency: less rapid change between sample values
* phase: relative shift or progression of a repeating event
* sequencer: configures the starting points and durations of sounds
* vocoder: splits into frequency bands and removes bands
* wave < instrument < composition
* more links
  * [amplitude](https://en.wikipedia.org/wiki/Amplitude)
  * [artificial reverberation](https://ccrma.stanford.edu/~jos/pasp/Artificial_Reverberation.html)
  * [beat](https://en.wikipedia.org/wiki/Beat_(acoustics)) interference pattern between two sounds of slightly different frequencies
  * [negative frequency](https://en.wikipedia.org/wiki/Negative_frequency)
  * [phase](https://en.wikipedia.org/wiki/Phase_(waves))
  * [rhythm](https://en.wikipedia.org/wiki/Rhythm)