[cdp] ZIGZAG times file

[Archer Endrich]

The excellent query recently about ZIGZAG shows that there is an 
ambiguity in the CDP documentation that needs to be clarified.

ZIGZAG lives up to its name:  it assumes that there will be a regularly 
alternating  forwards and backwards movement.  This is why it issues a 
warning when two successive times go in the same direction.

The times file is simply a series of times (not a time and a value), 
either in a line with the times separated by spaces, or as a column.  It 
could be described in words as:

time     earlier_time later_time earlier_time  later_time
2          1                      4 2.5                 6
forwards backwards    forwards   backwards     forwards
-> 2 sec  <- 1 sec    -> 4 sec   <- 2.5 sec    -> 6 sec   etc.

I tested some patterns using count.wav as the input soundfile (8 sec 
duration).

A pattern that moves from both ends towards the centre:
   0  8  1  7  2  6  3  5  4  4.5  [the output soundfile stops here]

Advancing through the file could be done with short backwards hops (some 
cool things happen at the turn points):
   0  2  1.8  3  2.8  4  3.8  5  4.8  7  6.8  8
  with the restriction that two different times must be greater than 3 
times the length of the splice;  if the splice is 15ms, the minimum time 
difference must be a little more than 45ms (about 0.045 sec) .

If the backwards movement isn't really wanted, EXTEND LOOP might be a 
better option.

The diagram in the manual is doing something like:
   forward to 3 seconds
   backwards to ca 1.5 sec
   forwards to 5 seconds
   backwards to ca 1.2 seconds
   forwards to end-of-(input)file

Its times file would therefore be:
   0  3  1.5  5  1.2  [the output soundfile stops here]
   (If the times file started at time 3 sec, the output soundfile would
   begin at time 3 seconds in the input file and immediately go backwards.)

I hope this clarifies the operation of this fun program.

Archer - CDP