Audio Digitizer and Encoder

Picolo U4 H.264 PCI-104 has 4 high-quality audio acquisition channels. Each audio channel converts a line-level analog audio signal into a digital audio stream.

A frequency synthesizer generates the master audio clock signal from a stable oscillator. Two master audio clock frequencies are available:

The frequency selection of the master audio clock is common to all the audio channels of a board. All the audio ADC's of the Picolo U4 H.264 PCI-104 are clocked at the same frequency.

The processing chain of each audio channel is composed of the following stages:

4 audio channels

Configurations

Available configurations of the audio channels

Sample rate (kHz)

Sample depth (bits)

Companding law

ADC clock

8

8

µ-law

48 kHz

8

8

A-law

48 kHz

8

16

PCM

48 kHz

16

16

Linear

48 kHz

22.05

16

Linear

44.1 kHz

44.1

16

Linear

44.1 kHz

48

16

Linear

48 kHz

Each audio channel is configured individually through the Virtual File System API.

The audio sampling frequencies of all the audio channels of a board must belong to one of the following two groups:

Volume Control

Each audio channel has an independent audio volume that can be modified any time. The volume adjusts the gain of the gain of the input amplifier.

The volume is controlled through the Virtual File System API.

The gain range of the volume control is sufficiently large to accept both "professional" and "consumer" line-level audio signal; however, it is not sufficient to allow direct connection of microphones. Refer to Audio Inputs Electrical Specifications applicable to the audio inputs of Picolo U4 H.264 PCI-104.

In order to optimize the signal-to-noise ratio, the user is invited to adjust the volume such that the highest amplitude of the incoming analog audio produces digital codes just below the maximum value.

The amplifier delivers a level-corrected analog audio signal to the A/D converter.