wvFilter

  wvFilter provides  filtering of sigTOOL waveform data

  Examples:
  channels=wvFilter(fhandle, source, target, Hd)
  channels=wvFilter(channels, source, target, Hd)

  where
          fhandle     is a sigTOOL data figure handle
                          source data will be taken from this figure and the
                          application data area will be updated with the
                          result
          channels    is a cell array of scchannel objects
          source      is the source channel number
          target      is the target channel to receive the result
                          (source and target may be equal)
          IntFlag     flag, true to convert to int16 on disc
          Hd          is a dfilt filter object

  wvFilter replaces wvFiltFilt and wvFFTFilt from earlier sigTOOL 
  versions

  For all filters, wvFilter will attempt to filter the data in RAM. If
  this fails because of out-of-memory errors, filtering will instead be
  performed on a temporary channel with data being stored on disc.

  FIR filters use a single pass through the data and correct for the
  group delay. Note however, that with an even number of filter
  coefficients, a shift of 0.5 samples will remain. Use filters
  with an odd number of coefficients to avoid this (i.e. specify an even
  order (n) in the design to get n+1 coefficients. FIR filters will be 
  applied using a fast FFT-based algorithm where this is possible and
  advantageous.

  IIR filters are applied using a double pass, zero-phase shift
  algorithm.

  For all filters, data are pre- and post -pended with a reversed and
  reflected copy of the data to minimize end-effects.

  See also filtfilt, filtfilthd, fftfilt, dfilt

  -------------------------------------------------------------------------
  Author: Malcolm Lidierth 11/08
  Copyright © The Author & King's College London 2008-
  -------------------------------------------------------------------------

  Revisions
    23.12.09  Add support for channel groups