code: def remix(signal, num_channels, channel=None):
      """
      Remix the signal to have the desired number of channels.
  
      Parameters
      ----------
      signal : numpy array
          Signal to be remixed.
      num_channels : int
          Number of channels.
      channel : int, optional
          When reducing a signal to `num_channels` of 1, use this channel,
          or 'None' to return the average across all channels.
  
      Returns
      -------
      numpy array
          Remixed signal (same dtype as `signal`).
  
      Notes
      -----
      This function does not support arbitrary channel number conversions.
      Only down-mixing to and up-mixing from mono signals is supported.
  
      The signal is returned with the same dtype, thus rounding errors may occur
      with integer dtypes.
  
      If the signal should be down-mixed to mono and has an integer dtype, it
      will be converted to float internally and then back to the original dtype
      to prevent clipping of the signal. To avoid this double conversion,
      convert the dtype first.
  
      """
      if num_channels == signal.ndim or num_channels is None:
          # return as many channels as there are.
          return signal
      elif num_channels == 1 and signal.ndim > 1:
          if channel is None:
              # down-mix to mono
              # Note: to prevent clipping, the signal is converted to float first
              #       and then converted back to the original dtype
              # TODO: add weighted mixing
              return np.mean(signal, axis=-1).astype(signal.dtype)
          else:
              # Use the requested channel verbatim
              return signal[:, channel]
      elif num_channels > 1 and signal.ndim == 1:
          # up-mix a mono signal simply by copying channels
          return np.tile(signal[:, np.newaxis], num_channels)
      else:
          # any other channel conversion is not supported
          raise NotImplementedError(
              "Requested %d channels, but got %d channels "
              "and channel conversion is not implemented."
              % (num_channels, signal.shape[1])
          )
  
imports: from __future__ import absolute_import, division, print_function
  import warnings
  import numpy
  from ..processors import BufferProcessor, Processor
  from ..utils import integer_types
label_desc: Use image node_id 5 for calling a global function with example usage: remix(signal, num_channels, channel) and returns: signal, np, signal, np