ONE:
The sample rate defines the number of samples per second of a digital audio file. A sample in digital audio is just a number but if draw a line connecting a great number of samples you would see a waveform. The higher the sample rate, the more samples there are in one second. The more samples, the better the representation of the acoustical waveform and therefore the higher the audio quality. Typical sample rates are 44.1kHz, 48kHz, 96kHz and 192kHz. KHz stands for 1000 per second. With a sample rate of 44.1kHz an audio file consists of 44100 samples per second.
In digital audio the bit depth describes how many bits are used for one sample. Similar to the sample rate, higher the bit depth, better the sound quality. The more numbers or bits we use for the scale the closer we can get to the actual amplitude. The closer we can get the smaller is the mistake we add to our audio signal. This mistake is called quantization noise. Therefore lesser the quantization noise, more accurate is the audio. Hence sample rate and bit depth are 2 important considerations in digitalization.

TWO:
TELEPHONES!
Speech signals, i.e., signals intended to carry only human speech, can usually be sampled at a much lower rate. For most phonemes, almost all of the energy is contained in the 5Hz-4 kHz range, allowing a sampling rate of 8 kHz. This is the sampling rate used by nearly all telephony systems, WALKIE TALKIEES AND WIRELESS INTERCOM., which use the G.711 sampling and quantization specifications. Where G.711 is an ITU-T standard for audio companding. It is primarily used in telephony
Telephone is historically in a 3000Hz range from 300Hz to 3300Hz, which covers the human voice, though