MAS3587F Datasheet, PDF (9/83 Pages) Micronas – Audio Encoder/Decoder

ADVANCE INFORMATION
MAS 3587F
2.5.2. Program Download Feature
The standard functions of the MAS 3587F can be
extended or substituted by downloading up to 4kWords
(1 Word = 20 bits) of program code and additionally up
to 4kWords of coefficients into the internal RAM.
The code must be downloaded by the Fast Program
Download command (see Section 3.3.1.14. on
page 31) into an area of RAM that is switchable from
data memory to program memory. A Run command
(see Section 3.3.1.1. on page 25) starts the operation.
2.6. Audio Codec
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).
Mic-In
Line-In
Output
Mic-Amplifier incl. Bias
A
Mono
D
A
D
Q-peak
Q-peak
Audio
Codec
D
A
Volume
D ^Balance
A
Mixer
Mono/Stereo
AVC
Bass/Treble
Loudness
MDB
Right invert
Fig. 2–4: Signal flow block diagram of Audio Codec
2.7. 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.
2.7.1. Baseband Processing
The several baseband functions are applied to the dig-
ital audio signal immediately before D/A conversion.
2.7.1.1. Bass, Treble, and Loudness
Standard baseband functions such as bass, treble,
and loudness are provided (refer to Table 3–12 on
page 43 for details).
2.7.2. Micronas Dynamic Bass (MDB)
The Micronas Dynamic Bass system (MDB) was
developed to extend the frequency range of loud-
speakers or headphones below the cutoff frequency of
the speakers. In addition to dynamically amplifying the
low frequency bass signals, the MDB exploits the psy-
choacoustic phenomenon of the ‘missing fundamen-
tal’. Adding harmonics 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
MDB, it can be customized to create different bass
effects and adapted to various loudspeaker character-
istics (see Section 3.4.4. on page 49).
2.7.2.1. Automatic Volume Control (AVC)
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 achieve a comfortable listening enjoyment.
The Automatic Volume Correction (AVC) solves this
problem by equalizing the volume level.
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 3–12 on page 43).
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.
output level
dBr
ON
−9
OFF
−15
−21
input level
dBr
−30 −24 −18 −12
−6
0 +6
Fig. 2–5: Simplified AVC characteristics
Micronas
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