Echo is a headache and frustration that often invades telephone communications. Echo is the phenomenon wherein speakers hear their own voice echoed back after a brief delay. Although some technologies mitigate many causes, echo is still a problem even with the advent of VoIP. Sidetone is a unique kind of echo where sound effectively loops back between the speaker and microphone at one end of a phone call.
Every telephone call has some echo, the question is whether that echo is apparent to the callers.
Echo is experienced in normal PSTN connections and also in VoIP connections, but due to the inherent delay in VoIP, it can actually be more noticeable. Echo that a caller hears is probably the result of the far-end, where an impedance mismatch bounces signals back from where they came, and in today’s global telecoms networks calls can transit a mixture of IP and PSTN network, on copper, fiber-optic, and wireless transmission legs. Due to notable delays, there are echoes of one's own words audibly discernable.
Research indicates that when there is a delay of 35ms or less in one-way transmission (round-trip delay of <70ms), the speaker cannot distinguish the echo from an acceptable level of sidetone. However, as one-way delay increases beyond 35ms, the echo grows more problematic. The longer the delay, the more dramatic and invasive the echo becomes.
Echo suppression and echo cancellation techniques are used in telephone systems and network infrastructure to maintain voice quality. These operate to prevent echo from being created or they remove it once detected. Echo suppression has been around since the 1950s and has evolved into echo cancellation, while also moving from largely hardware-based techniques to software-based techniques.
Much of the network equipment in the path between any two callers will have settings that can help manage and minimize echo, however, most phone calls involve multiple networks and each network will be managed by teams making different configuration choices. Echo remains an ever-present phenomenon.
Today’s users have very high expectations regarding the quality of phone calls, and there are many issues that can occur with a voice connection, including echo. Businesses depend on clear communication channels in their customer interactions and more and more are taking a truly proactive approach to audio quality management.
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