MAS 35x9F
DATA SHEET
2.4. Audio Codec
2.4.2.2. Micronas Bass (MB)
A sophisticated set of audio converters and sound fea-
tures has been implemented to comply with various
kinds of operating environments that range up to high-
end equipment (see Fig. 2–4).
The Micronas Bass system (MB) was developed to
extend the frequency range of loudspeakers or head-
phones below the cutoff frequency of the speakers.
Apart from dynamically amplifying the low-frequency
bass signals, the MB exploits the psycho-acoustic phe-
nomenon of the ‘missing fundamental’. Adding har-
monics of the frequency components below the cutoff
frequency gives the impression of actually hearing the
low frequency fundamental, while at the same time
retaining the loudness of the original signal. Due to the
parametric implementation of the MB, it can be cus-
tomized to create different bass effects and adapted to
Mic-In
Mic-Amplifier incl. Bias
Mono
A
D
D
Line-In
A
various
loudspeaker
characteristics
(see
Section 3.4.4. and Table 3–16).
Mixer
Q-peak
Mono/Stereo
AVC
2.4.2.3. Automatic Volume Control (AVC)
Q-peak
In a collection of tracks from different sources fairly
often the average volume level varies. Especially in a
noisy listening environment the user must adjust the
volume to comfortably enjoy listening. The Automatic
Volume Correction (AVC) solves this problem by
equalizing the volume level.
Bass/Treble
Audio
Codec
Loudness
MB
Right invert
D
D
A
Volume
Balance
To prevent clipping, the AVC's gain decreases quickly
in dynamic boost conditions. To suppress oscillation
effects, the gain increases rather slowly for low level
inputs. The decay time is programmable by means of
the AVC register (see Table 3–16 on page 46).
Output
A
Fig. 2–4: Signal flow block diagram of Audio Codec
For input levels of -18 dBr to 0 dBr, the AVC maintains
a fixed output level of -9 dBr. Fig. 2–5 shows the AVC
output level versus its input level. For volume and
baseband registers set to 0 dB, a level of 0 dBr corre-
sponds to full scale input/output.
2.4.1. A/D Converter and Microphone Amplifier
A pair of A/D converters is provided for recording or
loop-through purposes. In addition, a microphone
amplifier including voltage supply function for an elec-
tret type microphone has been integrated.
AVC
output level
dBr
off
AVC
on
2.4.2. Baseband Processing
−9
The several baseband functions are applied to the dig-
ital audio signal immediately before D/A conversion.
−15
−21
2.4.2.1. Bass, Treble, and Loudness
input level
dBr
−30
−24
−18
−12
−6
0
+6
Standard baseband functions such as bass, treble,
and loudness are provided (refer to Table 3–16 for
details).
Fig. 2–5: Simplified AVC characteristics
2.4.2.4. Balance and Volume
To minimize quantization noise, the main volume con-
trol is automatically split into a digital and an analog
part. The volume range is −114...+12 dB with an addi-
tional mute position. A balance function is provided.
10
June 30, 2004; 6251-505-1DS
Micronas
MICRONAS [ MICRONAS ]
