Audio Controls
Volume Control
The MP3 decoder implements volume control on both right and left channels. The
MP3VOR and MP3VOL registers allow a 32-step volume control according to Table 71.
Table 71. Volume Control
VOL4:0 or VOR4:0
00000
Volume Gain (dB)
Mute
-33
-27
-1.5
0
00001
00010
11110
11111
Equalization Control
Sound can be adjusted using a 3-band equalizer: a bass band under 750 Hz, a medium
band from 750 Hz to 3300 Hz and a treble band over 3300 Hz. The MP3BAS, MP3MED,
and MP3TRE registers allow a 32-step gain control in each band according to Table 72.
Table 72. Bass, Medium, Treble Control
BAS4:0 or MED4:0 or TRE4:0
Gain (dB)
- ∞
00000
00001
00010
11110
11111
-14
-10
+1
+1.5
Special Effect
The MPBBST bit in MP3CON register allows enabling of a bass boost effect with the fol-
lowing characteristics: gain increase of +9 dB in the frequency under 375 Hz.
Decoding Errors
The three different errors that can appear during frame processing are detailed in the
following sections. All these errors can trigger an interrupt as explained in Section "Inter-
rupt", page 66.
Layer Error
The ERRSYN flag in MP3STA is set when a non-supported layer is decoded in the
header of the frame that has been sent to the decoder.
Synchronization Error
CRC Error
The ERRSYN flag in MP3STA is set when no synchronization pattern is found in the
data that have been sent to the decoder.
When the CRC of a frame does not match the one calculated, the flag ERRCRC in
MP3STA is set. In this case, depending on the CRCEN bit in MP3CON, the frame is
played or rejected. In both cases, noise may appear at audio output.
64
AT8xC51SND2C
4341D–MP3–04/05
ATMEL [ ATMEL ]
