Audio Engineering Society

Topic: The Psychoacoustics of Phase

Presented by: Jon Boley

The January 29, 2014, meeting of the Chicago AES Section was held at Shure Incorporated, located in Niles, Illinois. Twenty seven members and sixteen non-members attended the meeting which included Jon Boley’s presentation entitled, ‘The Psychoacoustics of Phase’.

This year our section has been able to make A/V recordings of our meetings and presentations - see below Additionally, Jon provided a link to view his slides:

Jon Boley began his presentation by describing the fundamentals of phase. He offered the visual of a single point on a rotating wheel and observing the path it takes through a full rotation. In this manner he described the attributes of amplitude and frequency. Phase-shifts could be referenced as moving forwards or backwards in time and interference could be considered either constructive or destructive.

Jon described a few typical applications: comb filter (delay a signal relative to itself); general digital filter (a general FIR filter includes lots of phase shifts or ANC, Active Noise Cancellation, provides a result when ‘anti-noise’ is added to noise); phase delay (identifying the phase at each frequency) versus group delay (identifying the negative derivative of the phase or the ‘slope’); and wave form delay (phase delay which delays the individual signal or group delay that delays the ‘envelope’ of the output signal).

After describing the fundamentals, Jon walked us through the ‘pyschoacoustics of phase’ – which was why, I think, many of us bought our tickets…now on to the ‘good stuff’. He referenced critical bands, AM (amplitude modulation) and FM (frequency modulation), and said that generally, within a critical band, it is easier to detect AM. In order to sense phase differences, one needs to be within a rather narrow frequency band. Phase changes manifest themselves as either a ‘modulated envelope’ or a ‘modulated frequency’. He offered and described several examples and scenarios such as: pitch, binaural pitch, loudness perception, masking, localization, speech, and neural phase detectors.

Jon concluded his presentation by offering three summary points: phase can be very important; phase itself can be audible; and phase information may be an important contributor to the ‘cocktail party’ effect.

The Chicago AES Section would like to extend a special thanks to Jon Boley for presenting to our section and joining several attendees for further conversation after the meeting at the restaurant next door to experience the ‘cocktail party’ effect in real time.

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