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AMBE-3000F™ Vocoder Chip Users Manual

Version 3.4, April, 2014

itial Design Considerations

r codec mode, the user must select two physical interfaces: one for the codec data and one for the packet data. The choices

for the codec interface are SPI or McBSP. The choices for the packet interface are McBSP or UART or Parallel Port. The

McBSP can not be used for both the codec interface and the packet interface.

For packet mode, the user must select one physical interface to be used for packet data. The packet interface is used to transfer

both the speech data samples and the compressed channel data. The choices for the packet interface are McBSP or UART or

Parallel Port.

The AMBE-3000F™ Vocoder Chip supports four separate physical interfaces: SPI, UART, Parallel port, and McBSP serial

port. The user must select a codec interface and a packet interface using hardware configuration pins IF_SELECT0 (TQFP

pin2, BGA pin C2), IF_SELECT1 (TQFP pin3, BGA pin C3), and IF_SELECT2 (TQFP pin4, BGA pin B1). The available

interface combinations are shown in Table 9 Physical Interface Selection

Interface Configurations

IF_SELECT Configuration

Pin #’s (TQFP / BGA)

Mode

4 / B1 3 / C3 2 / C2

Codec Interface Packet Interface

Codec Mode 0 0 0 SPI UART

Codec Mode 0 0 1 SPI PPT

Codec Mode 0 1 0 SPI McBSP*

Codec Mode 0 1 1 McBSP* UART

Codec Mode 1 0 0 McBSP* PPT

Packet Mode 1 0 1 Not used UART

Packet Mode 1 1 0 Not used PPT

Packet Mode 1 1 1 Not used McBSP*

Table 9 Physical Interface Selection

*Note: McBSP Interface may be used for codec interface or the packet interface but not both.

4.3 A/D – D/A Codec chip Selection

The AMBE-3000F™ Vocoder Chip can be configured to transmit and receive digitized speech to and from most linear, a-law,

or u-law A/D-D/A codecs. The format of the incoming and outgoing speech data streams are coupled, that is to say they must

be the same format (16-bit linear, 8-bit a-law, or 8-bit -law). The digitized speech from the external A/D is converted into

compressed digital data (encoded) by the AMBE-3000F™ Vocoder Chip and the channel data is output to the packet interface.

Alternatively, speech data can be sent to/from the AMBE-3000F™ Vocoder Chip via a packet interface.

The choice of the A/D-D/A chip is critical to designing a system with superior voice quality. Given that a-law and -law

companding chips are already incorporating some compression to reduce the number of bits per sample, it is recommended

that, when possible, a 16-bit linear device be used for maximum voice quality. When choosing a device, pay particular

attention to signal to noise ratios and frequency responses of any filters that may be present on the analog front end of these

chips. Generally speaking, the flatter the frequency response over the voice spectrum (20-4000Hz) the better the overall

system will sound. The a-law and law interfaces are mainly provided for the design engineer who is trying to fit to pre-

existing conditions or is under cost savings restraints.

4.4 Vocoder State

In systems that require the ability to encode/decode different subsequent audio streams the vocoder state in the AMBE-3000™

Vocoder Chip would need to be reset back to the initial state. This will ensure that new audio streams will not be using state

data from a previous unrelated audio stream. To clear out any old vocoder state information the designer should send a

PKT_INIT to the AMBE-3000™ Vocoder Chip in between each different audio stream. This will reset the chip back to the

default state and allow it to encode/decode properly.

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