Richard Heyser was fascinated by the link between time and frequency, via the Fourier and Hilbert transforms. During his lifetime, performing the Fourier transform was a difficult thing to do, and he developed novel techniques to allow us to measure the time and frequency characteristics of audio systems and studios. Nowadays, it is simple to perform Fourier transforms in real-time on readily available computer hardware. Much of our processing of signals in the audio chain is now done via the Fourier transform, and versions of it form the basis of our audio coding systems for audio delivery.
We also know that the inner ear of a human listener converts a time domain acoustic signal into a frequency-based representation before it encodes it into neural impulses. However, the inner ear’s frequency representation is different to that obtained from a Fourier transform.
The talk, which should be accessible to people from all the different areas of endeavor within the AES, will first examine the operation of the ear, including its dynamic non-linear behavior. It will then examine the difference between the Fourier Transform and the human auditory system and highlight how they trade off time and frequency resolution differently.
We will then look at how processing in the Fourier domain can result in artifacts that can be perceived by the ear and discuss how one could mitigate these effects in Fourier-based processing systems.
Finally, we shall look at the unique ways the human auditory system allows us to hear the incredible complexity of the audio signal and how that might affect what we do in the future to improve audio, and perhaps move closer to some of Richard’s final words: “Perhaps more than any other discipline, audio engineering involves not only purely objective characterization but also subjective interpretations. It is the listening experience, that personal and most private sensation, which is the intended result of our labors in audio engineering. No technical measurement, however glorified with mathematics, can escape that fact.”