Sony STR-DA5700ES - Manual (Page 14)

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DTS
Lights up when the receiver is decoding
DTS signals.
DTS-ES
Lights up with the either following
indicator, depending on the input signal
decoding format.
96/24
DTS 96/24 (96 kHz/24 bit) decoding
DISC
DTS-ES Discrete 6.1
MTX
DTS-ES Matrix 6.1
Z NEO:X
Lights up when DTS Neo:X Cinema/
Music/Game decoding is activated.