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Digital signals are susceptible to the same impairments as analog signals when they are transmitted over analog facilities. However, they are less susceptible to most impairments. Digital transmission can be designed to correct errors automatically. For example, digital information signals between computers may be transmitted along with error-detecting codes. When an error is detected, the information is retransmitted. The impairments over a digital transmission facility are digital attenuation and echo. Digital signals are subject to attenuation or signal loss. With digital transmission, regenerators are used to reconstruct, or regenerate, the digital signal.

Message circuit noise comes from several sources and includes local exchange battery/ground noise. Two other types of message circuit noise are Thermal noise and Impulse noise. Thermal noise, which is random noise that is generated when electrical circuit elements vary in temperature. Impulse noise, which includes noise generated because of power fluctuations and induced noise
spikes. Intelligible crosstalk is an understandable speech signal from one channel affecting adjacent channels. If channels are a separate pair of wires, EMR from a high amplitude wire affects adjacent low amplitude wire pairs. It also occurs when signals using Frequency Division Multiplexing vary beyond the bandwidth limits of their channels.

Delay is caused in some cases due to lower frequencies. Lower frequencies have less resistance in a metallic medium. Therefore, they arrive sooner at the receiver. This causes signals with different frequencies to arrive at the receiver at different times. The difference between the signal that reaches first and subsequent signals is called delay. Delay has no major effect on speech transmission if it is kept at 600 ms or less. Amplitude Frequency Distortion is present when a waveform is altered in amplitude, at a certain frequency, during transmission. This may happen in an unconditioned transmission line where, at a certain frequency, the amplitude is reduced.