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Some Symptoms that may help you describe the problem:
Absolute Silence - This type of silence between speech can be understood if you have ever had the experience of not knowing whether the other person is still there because there is no sound on the line.
Clicking - Clicking is an external sound similar to a knock that is inserted usually at intervals.
Crackling - Crackling is an irregular form of very light static, similar to the sound a fire makes.
Crosstalk - Crosstalk is a familiar concept where you can hear another conversation on the line. Commonly, the other parties cannot hear you. There are also forms of crosstalk where all parties can hear each other.
Hissing - Hissing is more driven and constant than static. White noise is a term often associated with strong hissing. Pink noise is a less constant hissing noise and brown noise even less constant still.
Hum - Hum is a buzzing noise of interference from an electromagnetic source. An example is the sound heard on a radio when a nearby mobile phone is about to be called or detecting a cell.
Popping - Popping is external sounds that are broader and less regular than clicking. This is similar to popping sounds that might be heard on a two-way radio.
Motor - motor sound is a severe distortion or a loud, rough, beating sound.
Static - Static is a granular distortion similar to bad reception on the radio.
The next set of problems relate to how you hear voice on the line.
Listener Echo - Listener and talker echo sound similar, although the signal strength of listener echo might be lower. The essential difference between them is who hears the echo and where it is produced. Listener echo is the component of the talker echo that leaks through the near-end hybrid and returns again to the listener, which causes a delayed softer echo. The listener hears the talker twice.
Talker Echo - Talker echo is the signal which leaks in the far-end hybrid and returns to the sender (talker). The talker hears an echo of his or her own voice.
Tunnel Voice - Tunnel voice is similar to talking in a tunnel or on a poor quality mobile phone car kit.
Choppy Voice - Choppy voice describes the sound when there are gaps in the voice. Syllables appear to be dropped or badly delayed in a start and stop fashion.
Clipped Voice - Clipping is where words are cut off. It can occur at the front-end or tail-end of a word. Sometimes it occurs at the beginning of a sentence.
Robotic or Synthetic Voice - The term synthetic means that the sound of the voice is artificial and with a quiver or fuzz. Predictive insertion causes this synthetic sound by replacing the sound lost when a packet is dropped with a best guess from a previous sample. Synthetic and choppy voice commonly occur together.
Underwater voice - This voice problem is similar to the sound of your voice when heard underwater.
Tinny voice - Tinny voice is similar to when you listen to an old-fashioned wireless broadcast.