SignalBase

SignalBase defines a basic API to inspect signals that are regularly sampled in time. It consists of the following functions.

• sampletype: a type T <: Number used to represent each sample, similar in purpose to eltype, but some signals may define these two functions differently.
• nchannels: the number of samples per frame
• framerate: the number of frames per second, can be a missing value.
• nframes: the number of frames; this can be a missing value
• duration: the duration in seconds of the signal (defaults to nframes(x) / framerate(x)). This value can be a missing value. This could be defined seperately from nframes if, for example, the framerate is unknown but the duration is known.

For example, one natural definition of an Array, interpreted as a signal would be as follows.

sampletype(x::Array) = eltype(x)
nchannels(x::Array) = size(x,2)
framerate(x::Array) = missing
nframes(x::Array) = size(x,1)

Such a definition is provided by SignalOperators.

This package also defines a set of utility functions for working with units relevant to signals via Unitful: namely, radians, frames, seconds and Hertz. The frames unit is newly defined here so that conversions between frames and units of time is convienient and unambiguous. The other three are already defined by Unitful. The following functions are available.

• inradians: converts a quantity to radians
• inframes: converts a quantity to frames
• inseconds: converts a quantity to seconds
• inHz: converst a quantity to Hertz

These functions apply the following phillosophy: units can be useful as part of a public API, but they should be an optional feature. Therefore, if a value is passed with a given unit type (e.g. 1kHz), use it. If the value has no unit specified, assume a default unit type: e.g. inHz(10.0) would assume that 10.0 is in units of Hertz. The returned value for all these functions are in the stated units, as a Float64 value.

The utility functions all properly handle missing values.

To make use of the unit names themselves (e.g. s for seconds) you can add them via SignalsBase.Units. They are only exported in this sub-module to avoid pollutting the namespace with short unit names unless desired. The exported units are: kframes, frames, Hz, s, kHz, ms, dB, °, rad