This thesis reports on three studies of downtrend and normalisation in Hong Kong Can¬
tonese, with the goal of finding out what kind of frame of reference can be used to identify
and equate the same Cantonese tone in different positions-in-utterance.
Downtrend as a general tendency of pitch to lower throughout an utterance is known to
affect how an accent is realised. An accent is realised with a lower fO value late in an
utterance than early in the utterance. One approach is to treat downtrend as a phonetic
frame of reference so that different fO values of the same accent can be equated in terms
of the same phonetic specifications . One issue that this approach needs to deal with is
to characterise the phonetic frame of reference, and to decide which features in the f0
contour can be attributed to the phonetic specifications of accents.
Studies in tone normalisation showed that phonetic specifications of tones are consistent
and invariant across speakers after normalisation. Variations of f0 range and level was
factored out. By applying normalisation to downtrend data, it is expected to separate
out the phonetic specifications of tones from any modification of the frame of reference.
The results showed that downtrend resulted from modifications of local fO range and the
phonetic specifications of tones were consistent and invariant relative to the localised fO
range. The localised fO range as a frame of reference was found to be perceptually valid
and significant in tone identification.