Digital Dbb And Mute Circuit - Sony MZ-E30 Service Manual

The D/A converter is also incorporated with a digital DBB (Dynamic Bass Boost) and eight times over sampling digital
filter. These perform boosting of low bands and data filtering respectively using digital signals. The D/A converter also has a
deemphasis function, which is controlled using the emphasis ON and OFF signals output from Pin #• (EMP) of the DSP/
digital servo. The D/A converted analog signal is output to the headphone amplifier (IC302) via the VOLUME DOWN circuit
(Q301), which attenuates the audio signal boosted when DBB is ON, from Pins !¶ and !§ (A OUT L, AOUT R).
When the VOL button connected to the system controller is operated to control volume, the volume data is sent to the
ATRAC decoder block of the DSP/digital servo (IC601) via the serial bus (SBUS) and the volume is controlled by digital
signal processing inside the block.
Likewise for the beep sound when the remote operation button is operated, the data is sent to the DSP/digital servo (IC601),
the beep signal is generated inside the DSP/digital servo and output to the headphone via the D/A converter and headphone
amplifier.
7-3.

Digital DBB and Mute Circuit

Fig. 7-3. shows the digital DBB (Dynamic Bass Boost) and mute circuit.
The D/A converter (IC301) incorporates a digital DBB function which is switched ON/OFF using the DBB switch (S301)
connected to Pin !¡ (DBB0) and Pin !™ (DBB1).
Low bands are boosted using the digital signal.
When Pin !¡ is set to "H", at the reference level (–12 dB), signal is boosted by about 3.5 dB for 100 Hz. When Pin !™ is set
to "H", it is boosted by about 8.5 dB. When DBB is turned ON, Q301 connected between the D/A converter and headphone
amplifier (IC301) also is turned ON at the same time. As a result, R206 (15 kΩ) and R202 (6.8 kΩ) or R106 and R102 are
connected in parallel, and attenuate the volume boosted by the DBB to prevent clipping caused by the volume increasing and
excess input to headphone amplifier when the DBB is ON.
On the other hand, the headphone standby signal from Pin &º (HP STBY) or the mute signal from Pin ^ª (HP MUTE) of
the system controller is input to the headphone amplifier to turn the standby mode and mute. When the standby signal is set
to "H" or the mute signal is set to "L" as shown in the timing chart in the figure, the sound signal input from the D/A
converter is output from the headphone.
During wakeup, and immediately after the PLAY mode is set, the headphone is muted by the approximately 500 to 600 ms
mute signal output from the system controller to prevent the output of pop noise, etc.
— 33 —