Send Audio Processing

The Hx1 and Hx2 hybrid's send-to-caller audio processing consists of the following functions:

• Sample rate conversion

• High-pass filter

• Anti-Feedback, consisting of the “pitch” shifter and Acoustic Echo Canceler

• AGC/Limiter

Sample Rate Conversion

AES and analog input sources are sample rate-converted to the hybrid’s internal sampling rate of 48 kHz.

High-Pass Filter

A high-pass filter with a 300 Hz break frequency improves hybrid performance and enhances intelligibility by removing unnecessary low frequencies from the input audio. This filter is always enabled.

Feedback Reduction

The Hx has an Acoustic Echo Canceler (AEC) that improves feedback performance and cancels echo caused by "speaker to mic" acoustic coupling. The Hx also uses a "frequency shifter" - a Telos Alliance innovation - that inserts a small, unnoticeable, shift in frequency to the send audio to prevent feedback buildup when the system is used with open speakers.

Automatic Gain Control and Limiter

The AGC helps maintain consistent audio levels to the caller. This function is always enabled. At moderate levels, it is "AGC-like’" while at higher peak levels it is more "limiter-like". In addition to making levels more consistent to callers, it performs the protection limiting required to meet Telecom regulatory requirements.