SM5950AM Datasheet, PDF (12/20 Pages) Nippon Precision Circuits Inc – Asynchronous Sample Rate Converter

SM5950AM
Sample Rate Conversion
The input/output sample rate conversion ratio is variable over a range 0.45 to 2.205 times frequency. The input
sample rate (fsi) range is 20kHz to 100kHz, while the output sample rate (fso) range is 30kHz to 50kHz. Note
that the sample rate conversion ratio lower limit means that conversion from fsi = 96kHz to fso = 32kHz is not
possible.
Anti-aliasing filter selection
The following 6 filters are provided to function as anti-aliasing filters during sample rate conversion, where the
optimum anti-aliasing filter is automatically selected in response to the automatic measurement of the sample
conversion ratio between the input sampling frequency (on LRCI) and the output sampling frequency (calcu-
lated using SCKO as reference).
Filter mode fs conversion ratio (fso/fsi)
Selects range
1
1.0 to 2.205 times
2
0.91875 times
3
0.72562 times
4
0.66667 times
5
0.50000 times
6
0.459375 times
≥ 0.969697 times
0.864865 to 0.969697 times
0.711111 to 0.864865 times
0.627451 to 0.711111 times
0.492308 to 0.627451 times
≤ 0.492308 times
Conversion frequency
(example)
Up conversion
48.0 → 44.1
44.1 → 32.0
48.0 → 32.0
96.0 → 48.0
96.0 → 44.1
If the selected anti-aliasing filter fs conversion ratio and the actual sample rate conversion ratio do not match,
the following phenomena occur.
Conversion condition
Response generated
Actual sample rate conversion ratio is lower than the
selected filter conversion ratio.
High-frequency aliasing noise occurs in the audio band.
Actual sample rate conversion ratio is higher than the Primarily cuts high-frequency components in the audio
selected filter conversion ratio.
band.
If the fs conversion ratio is not fixed, the conversion will slowly follow the change in ratio, but in the process
the possibility exists that noise may occur in the audio data output.
NIPPON PRECISION CIRCUITS INC.—12