Digital Audio (2/2) S.P.Vimal CSIS Group BITS-Pilani

01/Feb/2007EA C473 -Multimedia Computing2 Topics today… DPCM & ADPCM DM & ADM Characterizing Sound

01/Feb/2007EA C473 -Multimedia Computing3 Differential Pulse Code Modulation (DPCM) Same as predictive coding, incorporates a quantizer (uniform or non uniform) Predictor is based on the reconstructed / quantized signal & the distortion is denoted by

01/Feb/2007EA C473 -Multimedia Computing4 Differential Pulse Code Modulation (DPCM) [2] The quantization steps can better be in the range of the signal Quantization steps can be modified as the coding progresses by estimating the mean and variance of the signal, keeping the objective function to be

01/Feb/2007EA C473 -Multimedia Computing5 Differential Pulse Code Modulation (DPCM) [3]

01/Feb/2007EA C473 -Multimedia Computing6 Differential Pulse Code Modulation (DPCM) [4] Assume the following predictor –And the difference being –Also assume the quantization scheme to be  –And

01/Feb/2007EA C473 -Multimedia Computing7 Differential Pulse Code Modulation (DPCM) [5] The above table is the result of Consider the sequence f 1 …f 5 =130,150,140,200,230 Initial confiq Input f 2 Input f 3 Input f 4 Input f 3

01/Feb/2007EA C473 -Multimedia Computing8 Differential Pulse Code Modulation (DPCM) [6] Lossy / lossless??? Try exercise 14, chapter 6 of T1

01/Feb/2007EA C473 -Multimedia Computing9 Adaptive DPCM Two components Quantizer & Predictor can be made adaptive In Quantizer –Consider quantization errors & try to minimize over the range of samples In Predictor –The linear predictor would be –Use least square approach to find the best value for a i

01/Feb/2007EA C473 -Multimedia Computing10 Delta modulation (DM) Simplified DPCM 1-bit encoder Not suitable for fast changing signals Adaptive DM???

01/Feb/2007EA C473 -Multimedia Computing11 Delta modulation (DM) [2]

01/Feb/2007EA C473 -Multimedia Computing12 Characterizing sound Sound can be characterized by –Pitch Ear’s response to the frequency is the perceived frequency Place theory provides the models that describe the relative pitch of two tones, not to describe the perfect/absolute pitch. Just noticeable difference in pitch is expressed in terms of cents & the standard figure for human ear is 5 cents

01/Feb/2007EA C473 -Multimedia Computing13 Characterizing sound [2] –Loudness Subjective term describing the strength of ear’s perception to the sound, directly related to the intensity. Perceived sensitivity is logarithmically related to the increase in the sound intensity –Quality / timbre Sound "quality" or "timbre" describes those characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness It takes around 60ms to recognize the timbre of the sound –For more on sound physics,

01/Feb/2007EA C473 -Multimedia Computing14 Reference: Chapter 6 of T1