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Audio Codecs
Published in Francis F. Li, Trevor J. Cox, Digital Signal Processing in Audio and Acoustical Engineering, 2019
Analogue signal is fed into a 1-bit quantizer controlled by a clock fs. The 1-bit quantizer is simply a threshold and can be implemented by a comparator. The output is taken, integrated, and sent as negative feedback into the input to form a feedback loop. The negative feedback attempts to minimise the errors between input and output; in other words, to force the output to follow the input. The output is a clocked bi-level signal, i.e. a bit stream. The integrator accumulates the errors and makes the overall output equal to input, i.e. attempts to make the statistics of output equal to input. Clearly, an integrator and a low pass filter will recover the original analogue signal. The modulation is based on the error signals, i.e. the input and predicted output; hence, the difference, or delta modulation. The delta modulation is the basis of sigma-delta modulation. As we shall see, an addition, sum, or integration stage will turn the delta modulation into a sigma (sum) and delta modulation. In both modulation and demodulation, an integrator is needed, as illustrated in Figure 5.7. One can move the second integrator to the modulation stage and simplify the de-modulation (Figure 5.8).
Oversampling Data Converters
Published in Bang-Sup Song, Micro CMOS Design, 2017
The normal PCM coder (Nyquist-rate ADC) adds the quantization noise (Q) to the signal (X) to get the quantized (digitized) output Y, and the quantization noise is additive, and uniformly spread over the Nyquist band. On the other hand, the ΔΣ modulator modifies the quantization noise spectrum by the NTF. Therefore, the quantization noise can be reduced in the narrow signal band where the loop gain is high. There are two such types of coders (ADCs) that benefit from oversampling. One is the predictive coder called delta modulation that shapes the signal by quantizing the error. The drawback of the delta modulation is that the decoder needs an integrator to reconstruct the original signal. As the integrator is basically DC unstable, reconstructing the signal using an integrator is challenging. The other is the noise-shaping coder that shapes the noise instead and reconstructs the signal just using a DAC as shown in Figure 6.9. The signal subtraction at the input is Δ, and the high-gain LPF or integrator is Σ. Thus, this coding system is called ΔΣ modulation.
D
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
such that f (t )(t - to )dt = f (to ). It is of relevance in defining the impulse response of a system. delta gun cathode ray tube (CRT) electron gun structure has the red, green, and blue electron gun components configured in the shape of an equilateral triangle; the structure provides the smallest CRT neck size and has the smallest deflection yoke diameter, but requires color registration (color convergence) correction in both the horizontal and the vertical CRT face. See cathode ray tube. delta modulation a special case of differential pulse code modulation (DPCM) where the digital code-out represents the change, or slope, of the analog input signal, rather than the absolute value of the analog input signal. A "1"
An efficient two-digit adaptive delta modulation for Laplacian source coding
Published in International Journal of Electronics, 2019
Zoran Peric, Bojan Denic, Vladimir Despotovic
Delta modulation (DM) is a simple analog-to-digital conversion technique that encodes only the sign of the signal slope, i.e., the information if the sample amplitude has increased or decreased relative to the previous sample. It can be considered as the simplest form of Differential Pulse Code Modulation (DPCM), with one-bit quantization and the first-order prediction (Chu, 2003; Gibson, Berger, Lookabaugh, Baker, & Lindbergh, 1998; Jayant & Noll, 1984; Sayood, 2005; Zrilic, 2005). Both DPCM and DM belong to a group of predictive coding algorithms (Atal, 2006; Gibson, 2016; Vaidyanathan, 2008). The conventional version of DM, also known as Linear Delta Modulation (LDM) is characterized by low complexity of encoder-decoder design and low-bit rate. However, the main drawback of LDM is the slope overload distortion caused by an inadequate step size choice, reflected in its inability to properly track the input signal variations, especially with the sudden signal changes (e.g. black- to-white transition in video or shouting voice in speech).