The Real Waveform Matters
The Samples Are Not Always What They Seem
Shannon-Nyquist sampling is so pervasive that we forget that, like any theory, there are terms and conditions attached. It assumes the signal is processed in a linear fashion. The minute these assumptions are violated, they break down and knowledge of the waveform the samples represent is required.
One example is the simple act of measuring a waveform’s level as used in many audio applications.
However, because the audio waveform is sampled the actual level may not be the sample values, but instead may be an intermediate value between the samples that may be higher, or lower, than the adjacent samples.
This talk, which will be accessible to a wide variety of backgrounds, will first discuss the issue involved in deriving the true signal value from the sampled audio, as a tutorial example of why sometimes it is necessary to reconstruct the analogue waveform to achieve accurate signal processing.
The pros and cons of various methods of measuring the peak value will be discussed, including alternative approaches that provide accuracy with low computation and delay. We will also look at other ways of obtaining the real waveform that can be used to efficiently extract real waveform values and apply this to frequency domain techniques as well.
Finally, we will conclude with a discussion of how the knowledge of the real sample values are required for other non-linear operations and suggest some methods of achieving this.
Jamie Angus-Whiteoak
Jamie Angus-Whiteoak is Emerita Professor of Audio Technology at Salford University. Her
career in industry and academia has spanned integrated optics, acoustics, analogue and
digital signal processing, and her expertise ranges from valve (tube) circuits to the applications
of esoteric number theory in signal processing. Jamie has invented modulated, wideband, and
absorbing diffusers, direct processing of Super Audio CD signals, and one of the first 4-
channel digital tape recorders. She worked in signal processing, analogue circuit design, and
numerous other audio technology topics, and has been active throughout the AES for 30
years. Aside from pioneering degree-level courses in both music technology and electronic
engineering in the UK, Jamie has been awarded an AES fellowship, the IoA Peter Barnett
Memorial Award, and the AES Silver and Gold Medal Awards "For extraordinary contributions as an innovator and inventor in the fields of audio science, acoustics, and signal processing".
She is also an honorary fellow of the IOA and ISCVE and is currently AES VP for Northern Europe.