Reverberations do not usually have enough distance or time to travel which means they can pile up on each other making it very difficult to comprehend. Echoes can be used to determine the distance of a reflecting object such as a large building or mountain if the ambient temperature and humidity are known. Reverberation does not allow enough travel time to use it to measure distance.
With reverberation, sound waves pile on top of each other arriving at the receiver or ear at different times making it difficult to comprehend or understand. The piling up of soundwaves also increases the sound energy in a room. The greater the round trip delay and impedance mismatch, the worse the potential echo. A similar path is established in between Phone B and Phone A.
A hybrid circuit does not create a brick-wall echo. A brick wall echo refers to one where the response of a far end impulse would be an echoed impulse. Since the hybrid is a circuit, the impulse response of the echo path is of a diffuse nature. The impulse response of the hybrid circuit is referred to as the echo tail. The duration of the echo tail is referred as the tail length. An echo canceller must cancel the entire tail.
To make matters more interesting, it is possible that multiple echo sources can be present within the tail circuit. This situation is referred to as one with multiple echo tails.
A good echo canceller will cancel echo due to all the echo sources in the network. Tail lengths exceeding 16 msec, up to msec are considered Long Tail Network. Echo tail to msec arehandled with the G. The terminology Near End and Far End are usually used when referring to an echo canceller.
For example, the Far End signal enters echo canceller A and passes through unchanged and is sent out to the hybrid. The hybrid, which is at the Near End with respect to echo canceller A, reflects a portion of the far end signal back towards the echo canceller. If echo cancellation is not performed and the network delay is moderate , the speaker at Phone A will perceive his echo.
Likewise, it is the responsibility of Echo Canceller A to cancel the echo that is induced by Hybrid A. As each hybrid circuit is slightly different, each echo tail is different as well.
Many factors determine the echo path. It is even possible for an echo tail to change while a circuit is active. This could happen when a second telephone extension is taken off-hook in parallel with the first one. Due to these variations in echo tails, it is necessary for an echo canceller to adapt to the tail continuously.
Adaptive Filtering is employed within echo cancellers to this end. The adaptive filters should converge quickly, but not so quickly that they might diverge under some conditions. This is especially important when a circuit is first established. Although the direction of the sound changes, the echo sounds the same as the original sound. Echoes can be heard in small spaces with hard walls, like wells, or where there are lots of hard surfaces all around.
That is why echoes can be heard in a canyon, cave, or mountain range. But sounds are not always reflected. When the sound later comes out in a room, there is additional echo. This is called acoustic, or spatial, echo. The solution to this is echo cancelling. Do you want to hear me talk about echo and listen to some examples?
Check out this video that covers it all. On this exiting trip into the world of sound and acoustics Dr Sound will focus on explaining the concept of Dr Sound is back with a new episode and subject this time is a really exciting and interesting one called In this fifth episode of Dr Sound Audio Academy you will be educated on a topic familiar to everyone.
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