This study develops an analytical procedure for predicting perceptual confusions of speech sounds in noise. The focus of the study was the perceptual role of formant frequencies higher than F2 in signalling the place of articulation for the stop consonants /b,d/ in /Co/ syllables. An identification experiment in which the stimuli were synthetic syllables mixed with a band-pass noise masker was conducted. The masker was centered around the F2 region. A perceptual metric was developed to analyze the results of the experiment. The metric was based on a combination of theoretical and empirical results and considered both within-hand and above-band masking of the formant frequencies. Results show that listeners were able to distinguish /be/ and /Aof syllables even when the entire F2 trajectory was predicted to be masked. Amplitude differences in F3 and F4 appeared to be used as place cues, even though the trajectories of these formants were the same for the two consonants.