Yamaha DSP-A990 Operation Manual page 6

When you notice that remote control operation has become
erratic, or the distance from which the remote control will function
has decreased, it's time to replace the batteries. Always replace all
batteries at the same time.
Make sure that the YPC/USER/LEARN switch on the remote
control unit is set to the YPC or USER position for normal
operation.
This remote control uses an advanced, highly directional infrared
beam. Be sure to aim the remote control directly at the remote
control sensor on the main unit when operating.
Remote control transmitter operation range
Notes
There should be no large obstacles between the remote
control transmitter and the main unit.
If the remote control sensor is directly illuminated by strong
lighting (especially an inverter type of fluorescent lamp etc.),
it might cause the remote control transmitter to work
incorrectly. In this case, reposition the main unit to avoid
direct lighting.
4
Remote control
sensor
Within approximately
6 m (19.7 feet)
Digital Sound Field Processing
What is it that makes live music so good? Today's advanced
sound reproduction technology lets you get extremely close to the
sound of a live performance, but chances are you'll still notice
something missing, the acoustic environment of the live concert hall.
Extensive research into the exact nature of the sonic reflections that
create the ambience of a large hall has made it possible for Yamaha
engineers to bring you this same sound in your own listening room,
so you'll feel all the sound of a live concert. What's more, our
technicians, armed with sophisticated measuring equipment, have
even made it possible to capture the acoustics of a variety of actual
concert halls, jazz clubs, theaters, etc. from around the world, to
allow you to accurately recreate any one of these live performance
environments, all in your own home.