Notes, Resources, Additional Information; The Acoustic Echo Canceller - Telos VX User Manual

|
49
5
notes, Resources,
Additional Information

The Acoustic Echo Canceller

You can learn how to connect the Acoustic Echo Canceller to your studio equipment in the
Studio Configuration section. Here, we provide more detail on how it works and how to use it.
A common annoyance in radio studio and TV studio operations is the feedback that often
results from using a loudspeaker to listen to telephone calls. This comes from the acoustic
coupling of the audio from the loudspeaker to the studio microphone that feeds to the caller.
As well, echo might be heard by the caller. When a caller talks, the phone audio bounces
around the studio and gets sent back. Due to the time-dispersion caused by the room and the
round-trip transmission delay, this acoustic echo is distracting to the caller.
In the past, when analog Telco lines were the norm and mobile phones were not yet attached
to everyone's ears , feedback was the usual problem, not echo per se. In earlier Telos hybrids,
we addressed that with a combination of ducking, frequency shifting, and a basic canceller.
That worked pretty well in its day, but Mobile phones and VoIP connections impose much
more delay – and the problem has become more challenging. With the multiple-hundreds
of milliseconds latency that can occur these days, an effective canceller must be part of the
system when loudspeaker monitoring is expected.
Fortunately, technology has come to the rescue. Modern Acoustic Echo Canceling is the
answer. The audio at the studio microphone consists of the host's voice combined with the
unwanted telephone audio that is delivered to the room via the loudspeaker. An AEC removes
the loudspeaker audio, leaving only the host. It does so by synthesizing the transfer function
of the acoustic path. The reference (loudspeaker) signal is passed through this function and
subtracted from the microphone signal, thus canceling the echoed telephone part of what the
microphone picks up. AECs have been used in high-end audio and video conferencing systems
for many years. High-end broadcast hybrids and on-air systems such as the Telos Delta, 2x12,
and Nx12 have included a limited form of AEC. But only recently has AEC technology advanced
to the stage where it is truly effective. Thankfully, it comes just when the added delay of mobile
and VoIP connections make it near essential. The good news has been a result of both break-
throughs in the design of AEC algorithms and the ever-increasing power and lower-cost of the
processor chips that are needed to implement them.