1. What is frequency?
According to International System of Units, the frequency is measured in hertz and is defined as the number of cycles per second of a periodic phenomenon.
2. What is an Audio Frequency (Audible frequency)?
An audible frequency is a periodic vibration that is audible to average human ears. It is always between 20hz and 20KHz.
3. What is (voice) signal Processing?
When a system or a process is operating or analysing the (voice) signals in either discrete or continuous time to perform useful operations on those signals, it can be called as (voice) signal processing.
4. What is Bandwidth?
Bandwidth has a significance difference in definition and understanding in analog and digital world. Let's define as below.
5. What is Analog Bandwidth?
It is a measure of the range of signal frequencies that a system can process or a transmission line can carry. It is measured in hertz.
6. What is Digital Bandwidth?
It is the rate of data (binary digits) transfer or throughput of the communication endpoint, measured in bits per second.
7. What is a Voice signal & the significance of Nyquist Rate in voice processing?
In physical forms, the voice is defined as vibration of air on the continuous-time plane. This signal can be sampled into discrete-time plane for processing or storing in digitized form. The digitized signal can be "fully" converted back to continuous-time plane for signal reproduction as "original". This is possible only when the sampling rate exceeds twice the maximum frequency in the "original" signal on continuous-time plane. This signal is said to be a band limiting signal and the associated sampling rate is defined as Nyquist Rate.
8. What is a voice channel?
The analog bandwidth of a Voice signal is roughly 4khz, and those used in telephony systems varies between 300hz and 3300hz. So, when we convert these signals into the discrete-time plane, we should ideally sample them at 8khz (as per the Nyquist Rate). This means every sample is taken at 125 micro secs (1/8000) in the continuous-time plane. So, if 256 level is used to represent a sample, i.e. 8 bits, then 8000 samples per second will result in transmitting 64000 bits per second. A voice channel on the telecommunications domain requires a channel bandwidth of 64kbps.
9. What is multiplexing?
It is a concept of using a single/same carrier for multiple (voice) channels. In the analog world, multiplexing is performed by dividing the channel based on frequencies (FDM). On the other hand, multiplexing in the digitized world is performed by divided the carrier into multiple channels by time (TDM) .
10. What is a T1 carrier line?
As an example, for a 1.5Mbps telephone carrier, 24 voice channels (1500/64 = 24) can be multiplexed. This is nothing but a classical T1 line. A typical T1 frame has 193 bits (24 channels * 8bit) / 125uSec. A TDM network, in general, will be implemented with transmission technologies like X.25, Frame Relay, IDN, ISDN and SONET.
Thanks for reading Part 1
The subsequent posts will have more in-detail information about various aspects of the voice technology... Thank you!
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