Datasheet

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VS1053B OGG VORBIS ENCODER VSMPG
5.2 End-to-End Delay of a Streaming System
For a rough end-to-end delay estimate of a streaming Ogg Vorbis system, the following
formula can be used:
d =
4096×n
f
×b+4000
f
s
where
• d is the result in seconds.
• n
f
is bits 7:4 of SCI_AICTRL3, see Chapter 2.3.1. For this formula to work, you
must set the bits to a non-zero value.
• b = 1 if you do byte-aligned read operations as instructed in Chapter 2.3.3. Other-
wise b = 2.
• f
s
is the samplerate.
Example: A 16 kHz voice profile is used. SCI_AICTRL3(7:4) is set to 1 for minumum
delay. However, byte-aligned reads are not done. The system delay is:
d =
4096×1×2+4000
16000
= 0.76 s
Naturally, you still have to add your transmission link delay to this value.
5.3 Playback Speed Adjustment
VS1053b’s playback samplerate may be adjusted with the recommended VS1053b Patches
w/ FLAC Decoder package, downloadable from
http://www.vlsi.fi/en/support/software/vs10xxpatches.html .
The patch lets the user to adjust samplerate with approximately 2 PPM increments. For
details, read the documentation for the VS1053b Patches package, particularly Chapter
Sample Rate Finetuning.
Example:
you are encoding Ogg Vorbis data using XTALI=12.288 MHz at a nominal sample rate
of 44100 Hz. However, you have learned from Chapter 2.6, Samplerate Considerations,
the actual samplerate to be approximately 43885.7 Hz. How much do you need to adjust
the samplerate?
(
43885.7 Hz
44100 Hz
− 1) × 512000 = −2488
Thus, write -2488 to the VS1053b Patches package Sample Rate Finetuning adjustment
register.
Note: Adjusting the sample rate is a relatively expensive operation and it should not be
done more often than once every 10 ms, preferably even less often than that.
Rev. 1.70c 2012-11-16
Page 36(39)