Now when you record you won't hear the piano play. Press STOP when the external data is finished. This mode can also be used to overcome the usual half second time delay. The piano will now respond as fast as it can to incoming data, when not recording. The response time, however, depends on the velocity of the notes.
Later models have a similar method of recording external data.
Then press the start button and record. Again, you'll see the LED's respond to velocity input, and an indication of the available memory space. The adjustable range Is 0 - 700msec.