function III_psy_ratio() {
		this.thm = new III_psy_xmin();
		this.en = new III_psy_xmin();
	}
<PRE>
          res_factor is the percentage of the target bitrate that should
          be used on average.  the remaining bits are added to the
          bitreservoir and used for difficult to encode frames.

          Since we are tracking the average bitrate, we should adjust
          res_factor "on the fly", increasing it if the average bitrate
          is greater than the requested bitrate, and decreasing it
          otherwise.  Reasonable ranges are from .9 to 1.0

          Until we get the above suggestion working, we use the following
          tuning:
          compression ratio    res_factor
          5.5  (256kbps)         1.0      no need for bitreservoir
          11   (128kbps)         .93      7% held for reservoir

          with linear interpolation for other values.
</PRE>