SignalWire Work users can experience various audio issues, and the information listed below will help to identify the audio issues experienced, with descriptions and possible explanations.

Click on the noise or sound problem to hear a sample recording of each.

Noise - Any noise on the line or in a voicemail message in addition to the voice signal. Noise typically leaves the conversation intelligible but still far from excellent. Static, hum, crosstalk, and intermittent popping tones are examples where the calling and called parties can understand each other but with some effort. Some noises are so severe that the voice becomes unintelligible. One such example, among the samples provided in this document, is a motor sound.

Absolute Silence
Symptom - the experience of not knowing whether the other person is still there because there is no sound on the line
Cause - Voice Activity Detection (VAD) without comfort noise. The background noise is loud enough for the silence insertion to be noticeable but soft enough so that VAD is engaged.

Symptom - an external sound similar to a knock that is inserted usually at intervals.
Cause - clock slips or other digital errors are common causes

Symptom - an irregular form of very light static, similar to the sound a fire makes
Cause - poor electrical connections, in particular poor cable connections. Other causes are electrical interference and a defective power supply on the phone

Symptom - where you can hear another conversation on the line; other parties cannot hear you; also forms where all parties can hear each other
Cause - wires in close proximity, where the signal of one is induced into the other

Hissing w/Unintelligible Voice Symptom Recording
Hissing Periods
Symptom - more driven and constant than static; white noise is often associated with strong hissing; pink noise is less constant hissing noise and brown noise even less constant still/a driven white noise that overwhelms the voice/periods often occur between segments of speech rather than throughout the whole signal
Cause - Voice Activity Detection (VAD)/

Symptom - a buzzing noise of interference from an electromagnetic source (ex. sound heard on the radio when a nearby mobile phone is to be called or detecting a cell.)
Cause - an electromagnetic source or telephone cables run near power lines

Symptom - external sounds that are broader and less regular than clicking; similar to popping sounds heard on a two-way radio
Cause - a Cisco Unity NIC card problem that inserts extra popping sounds

Motor Sound
Symptom - a severe distortion or a loud, rough, beating sound
Cause - fast switched cRTP bug

Cause - Digital Signal Processor (DSP) bug or failure

Severe Static
Symptom - granular distortion similar to bad reception on the radio
Cause - electrical interference or Voice Activity Detection (VAD)

Voice Distortion - Typically any problem that affects the voice itself. Voice Distortion is further divided into 3 categories: Echoed Voice, Garbled Voice, & Volume Distortion.

Echoed Voice - when the voice signal is repeated on the line and can be heard at either end of the call, in varying degrees & w/ many combinations of delay and loss within the echoed signal.

Listener Echo
Symptom - sounds similar to talker echo but the signal strength might be lower; the component of the talker echo that leaks through near-end hybrid and returns again to the listener, which causes a delayed softer echo; the listener hears the talker twice
Cause - insufficient loss of the echo signal; long echo tail; echo cancellers in the gateway adjacent to the near-end hybrid not activating

Talker Echo
Symptom - the signal which leaks in the far-end hybrid not activating and returns to the sender (talker); the talker hears an echo of his or her voice
Cause - insufficient loss of the echo signal; echo cancellers in the gateway adjacent to the far-end not activating; acoustic echo caused by the phone of the listener

Tunnel Echo
Symptom - similar to talking in a tunnel or on a poor quality mobile phone car kit
Cause - tight echo with some loss; ex. 10 ms delay and 50% loss on the echo signal

Garbled Voice - where the actual character of the voice is altered to a significant degree and often has a quality that fluctuates. Sometimes, the voice becomes unintelligible.

Choppy Voice (Broken Voice)
Symptom - the sound when there are gaps in the voice; syllables appear to be dropped or badly delayed in a start and stop fashion
Cause - consecutive packets that are lost or excessively delayed, such that DSP predictive insertion cannot be used and silence is inserted instead (ex. delay inserted into a call through contention caused by large data packets

Clipped Voice
Symptom - 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
Cause - Voice Activity Detection (VAD)

Robotic Voice
Symptom - a special case of synthetic voice
Cause - the default playout delay was small enough to mean that jitter induced by Cisco Unity caused packets to be dropped and predictive insertion to occur

Synthetic Voice
Symptom - the sound of the voice is artificial and with a quiver of fuzz; predictive insertion causes this sound by replacing the sound lost when a packet is dropped with the best guess from a previous sample; commonly occurs w/ choppy voice
Cause - single packet loss or delay beyond the bound of the de-jitter buffer playout period; DSP predictive insertion causes the synthetic quality of the voice (ex. when a call is provided insufficient bandwidth)

Underwater Voice
Intelligible Underwater Voice / Unintelligible Underwater Voice]
Symptom - voice problem similar to the sound of your voice when heard underwater/describes a distortion that makes it impossible to understand the voice; descriptions are the sound of a cassette tape fast-forwarded, a gulping sound, and a wishy-washy sound/
Cause - a fast-switched cRTP bug


Volume Distortion - associated with incorrect volume levels, whether constant or in flux.

Fluctuating Voice
Symptom - when the volume of the voice increases & decreases in a wave fashion; if occurs rapidly it can be confused with some form of garbled voice
Cause - a bug w/ IP telephone load

Fuzzy Voice
Symptom - sounds similar to a radio turned up too loud and the voice is shaky; this might only occur at certain signal levels within the sentence; this depends on the level of gain applied
Cause - too much gain on the signal, possibly introduced at one of a number of points in the network (ex. the signal can be overdriven from the PBX of high gain through the Cisco Unity Tag-switched Path (TSP) setting

Loud Voice
Cause - too much gain on the signal, possibly introduced at one of a number of points in the network (ex. the signal can be overdriven from the PBX or high gain through Cisco Unity TSP setting

Muffled Voice
Symptom - sounds similar to when you speak w/ your hand over your mouth
Cause - overdriven signal or some other cause that eliminates or reduces signal level at frequencies inside the key range for voice

Soft Voice
Cause - too much attenuation on signal possibly introduced at one of a number of points in the network

Tinny Voice
Symptom - similar to when you listen to an old-fashioned wireless broadcast
Cause - an overdriven signal, or some other cause that eliminates or reduces

Information is taken from
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