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Sound quality considerations
Published in John Watkinson, The Art of Digital Audio, 2013
Convertors are also sensitive to unwanted signals superimposed on the references. In fact the multiplicative nature of a convertor means that reference noise amplitude modulates the audio to create sidebands. Power supply ripple on the reference due to inadequate regulation or decoupling causes sidebands 50, 60, 100 or 120 Hz away from the audio frequencies, yet does not raise the noise floor when the input is quiescent. The multiplicative effect reveals how to test for it. Once more a spectrum analyser is connected to the convertor output. An audio frequency tone is input, and the level is changed. If the noise floor changes with the input signal level, there is reference noise. RF interference on a convertor reference is more insidious, particularly in the case of noise-shaped devices. Noise-shaped convertors operate with signals which must contain a great deal of high-frequency noise just beyond the audio band. RF on the reference amplitude modulates this noise and the sidebands can enter the audio band, raising the noise floor or causing discrete tones depending on the nature of the pickup.
Sound quality considerations
Published in John Watkinson, The Art of Sound Reproduction, 2012
Converters are also sensitive to unwanted signals superimposed on the references. In fact the multiplicative nature of a converter means that reference noise amplitude modulates the audio to create sidebands. Power supply ripple on the reference due to inadequate regulation or decoupling causes sidebands 50, 60, 100 or 120 Hz away from the audio frequencies, yet does not raise the noise floor when the input is quiescent. The multiplicative effect reveals how to test for it. Once more a spectrum analyser is connected to the converter output. An audio frequency tone is input, and the level is changed. If the noise floor changes with the input signal level, there is reference noise. Radio frequency interference on a converter reference is more insidious, particularly in the case of noise-shaped devices. Noise-shaped converters operate with signals which must contain a great deal of high-frequency noise just beyond the audio band. Radio frequency on the reference amplitude modulates this noise and the sidebands can enter the audio band, raising the noise floor or causing discrete tones depending on the nature of the pickup.
Review of Fundamentals Related to DC Power Supply Design and Linear Regulators
Published in Nihal Kularatna, DC Power Supplies Power Management and Surge Protection for Power Electronic Systems, 2018
Although the above are the most important quality parameters of a voltage reference, noise is particularly of importance in certain applications such as A/D or D/A converters. In such applications, the noise from the reference should be less than 10% of the LSB value of the converter. Therefore the higher the resolution of the converter, the lower should be the noise generated from the reference. Noise depends on the operating current of the reference, and is generally specified over a particular bandwidth and for a particular current. The specified bandwidths are 0.1–10 Hz (low-frequency noise) and 10 Hz–10 kHz (high-frequency noise).
Design and testing of a personalized noise monitoring system
Published in Journal of Occupational and Environmental Hygiene, 2023
Oliver Stroh, Geb Thomas, Thomas M. Peters, Marcus Tatum
The minute averages were taken from the noise data for analysis, again excluding values below 60 dBA. Readings for the HearSafe device ranged between 56.19 and 95.26 dBA, where the dBadge ranged between 42.78 and 99.22 dBA with the averages being 76.50 and 78.24 dBA. The 5th percentile was 65.44 and 63.37, and 95th was 81.91 and 83.26 for the HearSafe and dBadge, respectively. Between the two instruments, there was a mean absolute error of 2.26 dBA and a mean error of −1 dBA, with 59% of the test instrument readings lying within ±2 dBA of the reference. A linear model was fit using the reference noise dosimeter’s data to predict the wearable device’s noise dosimeter data, again with no intercept, which is displayed in Figure 4. The root mean square error was 3.07, with an R2 value of 79.5%. The resulting slope was 0.985, which was significant using an alpha of 0.01.
Spectral trimming technique: a new approach for suppressing motion artefacts in stress electrocardiography
Published in Journal of Medical Engineering & Technology, 2020
A. S. Lakhe, R. K. Jain, Vineet Sinha, T. S. Anantkrishnan, P. P. Athavale, Bhaimangesh Naik, G. D. Jindal
Since signal components of ECG and motion artefacts overlap in the 0−2 Hz range, use of regular fixed and non-adaptive filters is expected to cause undesired loss of signal components along with desired suppression of artefacts. This has led to the development of adaptive filtering, which is advantageous in processing signals with unknown and time varying noise frequencies. The adaptive filters separate the embedded noise in the signal in relation with simultaneously recorded noise [4], fed to the reference noise input of adaptive filter; thereby preserving the physiological nature of the input signal. Widrow et al. [5] have been one of the earlier users of adaptive noise cancellation (ANC), which has been followed by many researchers to denoise ECG successfully [6–8]. The coefficients of the filter are updated by adaptive algorithm in order to minimise the error at the filter output. ANC appears to be method of choice for suppressing motion artefacts without significant loss of signal contents, but for requirement of an additional sensor (necessary for recording reference noise). In this respect, adaptive line enhancement (ALE) is more user friendly as it does not require reference noise input. In this method the corrupted input signal, is delayed in time (typically 0.02–0.50 s) and fed to reference noise input of the adaptive filter [9].
A Robust Adaptive Filter for Diffusion Strategy-based Distributed Active Noise Control
Published in IETE Journal of Research, 2023
In this section, two possible impulsive noise using model (34) were evaluated (a) , (b) . The impulsive noise is added at the output of the primary channel. As the parameter is reduced the impulsive noise increases. In the first case, the noise is less impulsive whereas increased intensity of impulsiveness is observed as the parameter increases. The simulation parameters for the input reference noise and output noise are given in Table 5.