When converting an analog signal (be it speech or another noise), you need to consider two important factors: sampling and quantization. Together, they determine the quality of the digitized sound.
Sampling is about the sampling rate — i.e. how many samples per second you use to encode the sound.
Quantization is about how many bits you use to represent each sample. The number of bits determines the number of different values you can represent with each sample.
Quantization
quantization is about how many bits you use to represent individual sound samples. In practice, we want to work with whole bytes, so let's consider 8 or 16 bits.
With 8-bit samples, each sample can represent 256 different values, so we can work with whole numbers between -128 and +127. Because of the whole numbers, it is inevitable that we introduce some noise into the signal as we convert it to digital samples. For example, if the exact analog value is "7.44125", we will represent it as "7". As we do this with each sample in the sequence, we slightly distort the signal — inject noise, in other words.
It turns out 8-bit samples do not result in a good quality. With only 256 sample values, the analog-to-digital conversion adds too much noise. The situation improves a lot if we switch to 16-bit samples as 16 bits give us 65536 different representations (from -32768 to +32767). 16-bit samples are what you will find on a CD and what VoIP codecs use as their input.
Sampling
With VoIP, you will most frequently encounter the sampling rate of 8 kilohertz. The frequency of 16 kHz can be used now and then in situations when a higher quality audio is required (with proportionally higher Internet bandwidth consumption).
The choice of sampling frequencies for the individual types of audio is not random. There is a rule (based on the work of Nyquist and Shanon) that the sampling frequency needs to be equal or greater than two times the transmitted bandwidth.
In short, It's good to remember that VoIP most frequently works with the sampling frequency of 8 kilohertz and each sample is stored in 16 bits.
references:
http://toncar.cz/Tutorials/VoIP/VoIP_Basics_Converting_Voice_to_Digital.html
Sampling is about the sampling rate — i.e. how many samples per second you use to encode the sound.
Quantization is about how many bits you use to represent each sample. The number of bits determines the number of different values you can represent with each sample.
Quantization
quantization is about how many bits you use to represent individual sound samples. In practice, we want to work with whole bytes, so let's consider 8 or 16 bits.
With 8-bit samples, each sample can represent 256 different values, so we can work with whole numbers between -128 and +127. Because of the whole numbers, it is inevitable that we introduce some noise into the signal as we convert it to digital samples. For example, if the exact analog value is "7.44125", we will represent it as "7". As we do this with each sample in the sequence, we slightly distort the signal — inject noise, in other words.
It turns out 8-bit samples do not result in a good quality. With only 256 sample values, the analog-to-digital conversion adds too much noise. The situation improves a lot if we switch to 16-bit samples as 16 bits give us 65536 different representations (from -32768 to +32767). 16-bit samples are what you will find on a CD and what VoIP codecs use as their input.
Sampling
With VoIP, you will most frequently encounter the sampling rate of 8 kilohertz. The frequency of 16 kHz can be used now and then in situations when a higher quality audio is required (with proportionally higher Internet bandwidth consumption).
The choice of sampling frequencies for the individual types of audio is not random. There is a rule (based on the work of Nyquist and Shanon) that the sampling frequency needs to be equal or greater than two times the transmitted bandwidth.
In short, It's good to remember that VoIP most frequently works with the sampling frequency of 8 kilohertz and each sample is stored in 16 bits.
references:
http://toncar.cz/Tutorials/VoIP/VoIP_Basics_Converting_Voice_to_Digital.html
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