Albalá Ingenieros AAC3008C01, Руководство пользователя, Страница: 20 / 32

Albalá Ingenieros | Manual AAC3008C01
4.2.4. Selection of the sampling frequency
The AAC3008C01 converter has two operating modes. The first is Automatic Mode, in
which the converter automatically selects the sampling frequency and the reference
input to lock to. The second mode is Manual Mode, where the user selects the
reference input and the sampling frequency.
4.2.4.1. Automatic Mode operation
When the AAC3008C01 operates in Automatic Mode, selection of the reference
source and the sampling frequency is performed automatically. The reference
signal is selected according to the following set of priorities:
- The AES/EBU digital audio reference.
- The black burst video input.
- The word-clock input.
- If no reference signal is available, the AAC3008C01 uses a sampling frequency
of 48kHz and its own internal oscillator.
The AES/EBU digital audio reference input accepts signals with or without audio.
The sampling frequency of this input is used as the reference for the internal
oscillator of the AAC3008C01. In this way all the standard frequencies are
generated: 32kHz, 44.1kHz, 48kHz, 64kHz, 88.2kHz and 96kHz. The PLL of the
AAC3008C01 will not be able to lock to any digital audio reference signals with
sampling rates other than the standard ones listed, and in such cases the
corresponding REFERENCE LED will blink.
The video input accepts signals of 525 or 625 lines. If this input is used as a
reference and the converter is in Automatic Mode then a sampling frequency of
48kHz is generated. The other standard sampling frequencies can be selected
when using Manual Mode.
The word-clock input accepts pulsed signals with TTL levels and whose frequency
must be among the standard values listed. The oscillator of the AAC3008C01 will
not be able to lock to any digital audio reference signals with sampling rates other
than the standard ones listed, and in such cases the corresponding REFERENCE LED
will blink.
The input video reference and the word-clock reference signals use the same
connector. The module can distinguish between the two signal types.
The margin in frequency for proper locking of the AAC3008C01 to reference signals
is ±40ppm.
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