DH 400

Digital Phone Hybrid with DSP echo canceller

What is the DSP echo cancellation ?

The Hybrid mission is to separate the telephone signal that travels toward the caller from the signal that returns from the caller to the console, preventing them from mixing. If you are using 2 pairs of wires all would be very simple (one way to go and another to return) but using only one pair, both signals are mixed. This occurs when we talk to the person remotely; a part of that signal returns with bad audio quality, affecting the local DJ voice on air.

Conventional Hybrids use an internal network that simulates the impedance of the phone line. This is only approximate and allows 15 to 30 dB of separation of signals. It is named rejection. The digital system converts the analog audio signal into a full digital one. It opens the possibility of a processing at the digital domain, for a perfect simulation of the real phone line. This allows not only simulate impedance, but time delays to create an exact replica of the returning signal. Then, we can sum it with inverted phase to cancel almost completely the annoying signal return.

The heart of the digital echo canceller is a FIR, taped delay line filter, of 256 steps. Each of them has a delay and contributes to the total sum through a variable multiplier coefficient. The output of this filter is compared with the input that we sent to a phone line (the speaker's voice from the radio) and automatically and dynamically these 256 coefficients are modified, using a LMS algorithm, to ensure that the response of this artificial line is exactly like the real telephone line. This adjustment is done in a couple of seconds at the conversation start.
The output of this line is then summed with inverted phase, to completely cancel the unwanted return.
The technology, created in the U.S. for satellite communications, is now available to your radio, incorporated into the DH400


DH400 is controlled by a mini-computer, which automates operations, allowing for very simple use by the operator or the local talent
	Illuminated push buttons allows for commute lines to OFF, Hold, On Air or Conference.



	Rear panel of DH400 with RJ11 connectors for telephone lines and balanced XLR output



	VQR: the magic of the restored sound quality

	DH400 incorporates the unique system: VQR of Solidyne, to restore the original voice quality that is lost through a telephone line or cellular. The phone quality is 300-3.400 Hz. But VQR synthesizes the bass and treble allowing obtain a final response from 50 - 12,000 Hz a near-studio audio quality If you wish knowing more about the VQR and listen to audio demos, click here

The DH400 is the integrated technology solution for the handling of the telephone lines in a excellence radio station