WM8734 ETC-unknow, WM8734 Datasheet - Page 27

• Manufacturer Part Number: WM8734
• Description: Stereo Audio Codec
• Manufacturer: ETC-unknow

WM8734
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USB MODE SAMPLE RATES
In USB mode the MCLK/crystal oscillator input is 12MHz only.
Notes:
1.
2.
3.
4.
The table above can be used to set up the device to work with various sample rate combinations. For
example if the user wishes to use the WM8734 in USB mode with the ADC and DAC sample rates at
48KHz and 48KHz respectively then the device should be programmed with BOSR = 0, SR3 = 0,
SR2 = 0, SR1 = 0 and SR0 = 0. The ADC and DAC will then operate with a Digital Filter of type 0,
refer to Digital Filter Characteristics section for an explanation of the different filter types.
The BOSR bit represents the base over-sampling rate. This is the rate that the WM8734 digital signal
processing is carried out at and the sampling rate will always be a sub-multiple of this. In USB mode,
with BOSR = 0, the base over-sampling rate is defined at 250fs, with BOSR = 1, the base over-
sampling rate is defined at 272fs. This can be used to determine the actual audio sampling rate
produced by the ADC and required by the DAC.
Example scenarios are, :-
1.
2.
Table 13 USB Mode Sample Rate Look-ip Table
(Note 2)
(Note 2)
(Note 1)
(Note 1)
(Note 3)
ADC
KHz
44.1
44.1
88.2
48
48
32
96
SAMPLING
8
8
8
8
with a requirement that the ADC data sampling rate is 8KHz and DAC data sampling rate is
48KHz the device is programmed with BOSR = 0 (250fs), SR3 = 0, SR2 = 0, SR1 = 1, SR0 =
0.The ADC will then be exactly 8KHz ( derived from 12MHz/250 x 1/6 ) and the DAC expects
data at exactly 48KHz ( derived from 12MHz/250 ).
with a requirement that ADC data rate is 8KHz and DAC data rate is 44.1KHz the device is
programmed with BOSR = 0 (272fs), SR3 = 0, SR2 = 0, SR1 = 1, SR0 = 0. The ADC will not
output data at exactly 8KHz, instead it will be 8.021KHz ( derived from 12MHz/272 x 2/11 ) and
the DAC at 44.118KHz ( derived from 12MHz/272 ). A slight (sub 0.5%) pitch shift will therefore
results in the 8KHz and 44.1KHz audio data and (more importantly) the user must ensure that
8k not exact, actual = 8.021kHz
44.1k not exact, actual = 44.118kHz
88.1k not exact, actual = 88.235kHz
All other combinations of BOSR and SR[3:0] that are not in the truth table are invalid
RATE
(Note 2)
(Note 1)
(Note 2)
(Note 1)
(Note 3)
DAC
KHz
44.1
44.1
88.2
48
48
32
96
8
8
8
8
FREQUENCY
12.000
12.000
12.000
12.000
12.000
12.000
12.000
12.000
12.000
12.000
12.000
MCLK
MHz
BOSR
0
1
0
1
0
1
0
1
0
0
1
SR3
REGISTER SETTINGS
0
1
0
1
0
1
0
1
0
0
1
SAMPLE
RATE
SR2
0
0
0
0
0
0
0
0
1
1
1
SR1
0
0
0
0
1
1
1
1
1
1
1
AI Rev 2.2 November 2001
Advanced Information
SR0
0
0
1
1
0
0
1
1
0
1
1
DIGITAL
FILTER
TYPE
0
1
0
1
0
1
0
1
0
3
2
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