Suppose we have many observations or many channels of
so we label them
We can define a model
Sometimes we have only a single signal
but it is quite long.
Because the signal is long, the magnitude of its Fourier transform is rough,
so we smooth it over frequency, and denote it thus:
These preliminary models are the most primative forms of deconvolved data. They deal only with the amplitude spectrum. Most deconvolutions involve also the phase. The generally chosen phase is one with a causal filter. A casual filter (vanishes before ) with FT is chosen so that is white. Finding this filter is a serious undertaking, normally done in a one-dimensional space. Here, taking advantage of the helix, we do it in space of any number of dimensions.
For reasons explained later, this is equivalent to minimizing the energy output of a filter beginning with a one, . The inverse of this filter is often called ``the impulse response'', or ``the source waveform''. Whether it actually is a source waveform depends on the physical setup as well as some mathematical assumptions we will learn.