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13 Cards in this Set

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 - To convert an analog signal to a digital signal, what are the 4 steps needed? C5 - 1 Sample the analog signal regularly; sampling rate must be twice the frequency - 2 Quantize the sample - 3 Encode the value into 8 bit digital form - 4 Compress the samples to reduce (or save) bandwidth. C5 - What is the most commonly used method of converting analog to digital signal? C5 - PCM – Pulse code modulation C5 - To convert a digital signal to an analog signal, what are the 3 steps needed? C5 - Decompress the samples (if compressed) - Decode the samples into voltage amplitudes, rebuilding the PAM signal - Filter the signal to remove any noise. C5 - Describe the Nyquist Theorem which is the basis for digital signal technology; C5 - If you sample an analog signal at twice the rate of the highest frequency of interest, you can accurately reconstruct that signal back into its analog form. C5 - What is quantization? C5 - It involves dividing the range of amplitude values that are present in an analog signal sample into a set of discrete steps that are closest in value to the original analog signal. C5 - Name 2 methods of quantization C5 - a-law (most countries) - u-law (Canada, U.S and Japan) C5 - The a-law and the u-law “compand” the signal; explain what this means. C5 - They both compress the signal for transmission and then expand the signal back to its original form at the other end. C5 - Name two types of voice-compression schemes; C5 - Waveform coding; (PCM,ADPCM) - Source coding;(LDCELP, CS-ACELP) C5 - What is a vocoder? C5 - A vocoder (or voice coder) is a device that converts analog speech into digital speech, using a specific compression scheme that is optimized for coding human speech. C5 - List 2 ITU standards (compression protocols-codec) for waveform compression scheme; C5 - G.711 rate 64 Kbps - G.726 rate can be 16,24 or 32 Kbps C5 - Name the compression algorithm that Cisco uses for high-quality 8 kbps voice; C5 - G.729 C5 - List the 3 common voice compression techniques standardized by ITU-T; C5 - PCM; Amplitude and voice signal is sampled and quantized at 8000 times per second. - ADPCM; Quantize the difference between the speech signal and a prediction that has been made of the speech signal - CELP; C5 - List 2 methods used to measure the quality of voice transported on a telephone line. C5 - Mean Opinion Score (M.O.S)- graded by humans and very subjective - Perceptual Speech Quality Measurement (P.S.Q.M) – works by comparing the transmitted speech to the original input and yields a score. - Note: Cisco voice equipment does not perfome voice quality measurements. C5