Aiwa NSX-MTD9 Operating Instructions Manual page 17

You can let the music start playing before performing step 1 or later at the desired moment.
1 Press BEAT ON/OFF to switch the function on.
You will hear the current rhythm pattern.
2 Turn MULTI JOG to select the desired rhythm pattern.
3 Press RHYTHM once while the selected rhythm pattern is displayed, then turn MULTI JOG to select
"AUTO".
While the unit is trying to get synced up to the tempo of the music, a cascade-like indicator will flash on the sides of
the graphic equalizer display section.
When the unit gets synced up to the tempo of the music, the display will momentarily read the synced-up tempo.
Depending on sound sources (such as, songs whose tempo is varying), however, you may see different tempos
appearing one after the other in the display.
After one synced up, if the sync lock unlocks, the display will read "BEAT OUT", and again the unit will try to get
synced up.
At the occurrence of BEAT OUT, the level of the rhythm is automatically reduced to "1"; and it increases back to the
preset level when sync is achieved again.
The BEAT function can be used together with the SPICE A/B function, as well as with the FILL IN function. But the
AUTO SPICE function cannot be used at the same time as the BEAT function.
SOUND (cont) PG. 10
USING THE FILL IN FUNCTION
The FILL IN function is used together with the BEAT function to insert a variation of the current rhythm pattern.