Receive Audio Processing

The Hx1 and Hx2 hybrid’s receive audio processing consists of the following functions:

• High-pass “hum” filter

• Adaptive Echo Cancellation

• Automatic Gain Control

• Noise Gate

• Digital Dynamic Equalization

• Sample rate conversion

High Pass Hum Filter

This filter removes hum and other unwanted low-frequency noise from the caller audio and has a break frequency of 100 Hz.

Adaptive Echo Cancellation

An adaptive filter removes studio send audio from the received caller audio. It adapts continuously to preserve a natural sound.

Automatic Gain Control

The Hx’s smart gated AGC improves the consistency of the caller’s audio level as delivered to the studio console without audible processing artifacts. An important feature of this AGC is that it is cross-coupled to other sections of the hybrids and can therefore reliably distinguish between caller audio and hybrid leakage. This allows the use of more aggressive gain control for bringing up low-level callers while still preserving excellent hybrid performance.

Noise Gate

Enabling the noise gate engages the built-in downward expander which reduces low-level line noise when no caller audio is present and reduces low-level leakage. This function is cross-coupled with the AGC and the ducking system.

Digital Dynamic Equalization

Telephone audio frequency response varies widely and is affected by many different factors. making some form of receive equalization desirable. The Hx’s Digital Dynamic EQ is the most sophisticated solution available in a broadcast telephone interface, and all processing is performed in the digital domain. The Receive EQ settings control the type of equalization applied to the receive telephone audio as follows:

• Off - Caller audio is passed without modification.

• Fixed - A simple manual equalizer.

• Adaptive (Digital Dynamic) - A three-band dynamic equalizer in which the frequency breakpoints, time constants, and other characteristics have been chosen to optimize the tonal quality of telephone callers; you set desired target levels to customize the caller's spectral characteristics, and the hybrid maintains the spectral balance from call to call.

• Adaptive + Fixed - This mode separately adds a fixed amount of additional gain to the high- and low-frequency bands of the three-band dynamic equalizer.