China
Africa
Explore chapters and articles related to this topic
Conversion
Published in John Watkinson, An Introduction to Digital Audio, 2013
The first documented use of dither was by Roberts17 in picture coding. In this system, pseudo-random noise (see Chapter 3) was added to the input signal prior to quantizing, but was subtracted after reconversion to analog. This is known as subtractive dither and has the advantages that the dither amplitude is non-critical and that the noise has full statistical independence from the signal. Unfortunately, it suffers from practical drawbacks, since the original noise waveform must accompany the samples or must be synchronously recreated at the DAC. This is virtually impossible in a system where the audio may have been edited or where its level has been changed by processing, as the noise needs to remain synchronous and be processed in the same way. Almost all practical digital audio systems use non-subtractive dither where the dither signal is added prior to quantization and no attempt is made to remove it at the DAC.18 The introduction of dither prior to a conventional quantizer inevitably causes a slight reduction in the signal-to-noise ratio attainable, but this reduction is a small price to pay for the elimination of non-linearities. The technique of noise shaping in conjunction with dither will be seen to overcome this restriction and produce performance in excess of the subtractive dither example above.
Audio Plug-ins
Published in Mike Collins, Pro Tools for Music Production, 2012
According to Ken Pohlmann in his book Principles of Digital Audio, ‘Without dither, a low level signal would be encoded by an A/D converter as a square wave. With dither, the output of the A/D is the signal with noise. Perceptually, the effects of dither are much preferred because noise is more readily tolerated by the ear than distortion.’ An added benefit of dither is that it lets the converter handle amplitudes below the lowest quantization value. As Pohlmann explains, ‘Dither changes the digital nature of the quantization error into a white noise and the ear may then resolve signals with levels well below one quantization level. So, with dither, the resolution of a digitization system is below the least significant bit. By encoding the audio signal with dither to produce modulation of the quantized signal, we may recover that information, even though it might be smaller than the smallest increment of the quantizer.’
Digital audio signals
Published in John Watkinson, The Art of Sound Reproduction, 2012
The first documented use of dither was by Roberts7 in picture coding. In this system, pseudo-random noise with rectangular probability and a peak-to-peak amplitude of Q was added to the input signal prior to quantizing, but was subtracted after reconversion to analog. This is known as subtractive dither and was investigated by Schuchman8 and much later by Sherwood.9 Subtractive dither has the advantages that the dither amplitude is non-critical, the noise has full statistical independence from the signal5 and has the same level as the quantizing error in the large signal undithered case.10 Unfortunately, it suffers from practical drawbacks, since the original noise waveform must accompany the samples or must be synchronously recreated at the DAC. This is virtually impossible in a system where the audio may have been edited or where its level has been changed by processing, as the noise needs to remain synchronous and be processed in the same way. All practical digital audio systems use non-subtractive dither where the dither signal is added prior to quantization and no attempt is made to remove it at the DAC.11 The introduction of dither prior to a conventional quantizer inevitably causes a slight reduction in the signal-to-noise ratio attainable, but this reduction is a small price to pay for the elimination of non-linearities. The technique of noise shaping in conjunction with dither will be seen to overcome this restriction and produce performance in excess of the subtractive dither example above.
A Low-distortion Hardware Efficient MASH
Published in Smart Science, 2018
Rijo Sebastian, Babita Roslind Jose, T. K. Shahana, Jimson Mathew
Figure 2 shows the improved MASH 2-1 architecture. This proposed architecture utilizes the improved feed-forward topology and it offers many advantages. This third-order modulator attains an enhanced fourth-order noise shaping with fewer active blocks. A portion of the second-stage quantization noise injected into the first stage acts as a dither signal there. Moreover, the unity signal transfer function (STF) relaxes the analog circuit non-idealities. A shifted loop delay topology, introduces delay in the feedback path, which is used to relax the signal processing timing for digital to analog conversion (DAC) and dynamic element matching techniques (DEM). In this architecture, the adder block before the quantizer is shifted to the input of second integrator and an extra feedback path is inserted in the modulator loop. This saves one power hungry feed-forward active adder required in multi-bit quantization. The mathematical analysis of the proposed modulator shows, how a third-order modulator can achieve a fourth-order NTF using inter-stage feedback paths. The output of first and second stage of MASH structure is given by