Glossary of Terms

Aliasing. The method of sampling often introduce side-effects like aliasing. A bad AD converter may produce false signals when there exists frequencies higher than half the sampling frequency. These may sound random to the ear, but can be described:

ffalse = fsampling - freal

Therefor one must filter out such frequencies before sampling. A "virtual" filtering must also be performed when doing a re-sampling (se "Re-sampling").

dB Decibel. In audio application a measurement of volume. The dB scale is a relative scale, where a fixed reference volume is needed. To state that two digital sounds differ 6dB means that the waveforms peak-to-peak appearance is twice as high. In describing the volume of one waveform, the reference is the maximum possible peak-to-peak appearance, and as every part of the waveform only can be smaller than the maximum, every volume will have a negative number. If the volume is -12 dB, it means that the waveform is 1/4 as high as possible.

A sound in "CD quality" has 16 bits of representation. In the digital world, every bit can double the height of the waveform. Therefor, a CD quality sounds is said to have (16 bits x 6 dB) 96dB dynamic range.

Fast fourier transform (FFT) An algorithm for performing a fourier transform. Generally, a FFT algorithm demands that the number of samples used is a power of 2 (2, 4, 8 ... 1024, 2048 ...).

Fourier, Jean-Babtiste Joseph (1768-1830). A French physicist and matemathician. Father of the Fourier analysis, which makes it easy to analyze the frequencies of a sound.

Nyquist frequency. When sampling at a sampling-frequency at 44.1kHz, one can only represent audio frequencies of 22.05kHz or lower. The Nyquist frequency is half the sampling frequency. This is because, to represent something oscillating (like a wave), one needs at least two samples.

Plugin An effect or file format that can be added after the installation of Pristine Sounds. An effect is a file named *.Plugin, and a file format *FileFormat. These files is in the plugin directory.

Re-sampling. When Changing the playback frequency of a sound without altering the speed or pitch, one must perform a virtual digital-to-analog conversion so a new (virtual) analog-to-digital conversion can take place.

Different approaches to do the virtual digital-to-analog process exist, where the best are the ones producing the least side-effects; aliasing.

Window function. When performing an FFT, a windowing function can be helpful to suppress unwanted side effects.

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