LED toggles the LED filter that controls the high-pass frequency filter.
Turning the LED off usually improves the sound.

LED is a replacement for the ultra-lengthy C version of LED (48 bytes v.
1088).  Sure, that's not much, but I'm a believer in efficiency. :) It is
rather ridiculous to write LED in C to begin with because it just takes
two commands in ML to do it.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                   33      48  68.8% -lh1- 6438 Feb 20  1992 led
[generic]                  428     628  68.2% -lh1- d102 Feb 20  1992 LED.doc
[generic]                  282     369  76.4% -lh1- f022 Feb 20  1992 LED.s
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         3 files     743    1045  71.1%            Feb 20  1992