B. Equipment

A 24-bit sound card (Babyface, RME, Germany) was used to generate the stimuli. The stimuli were presented unilaterally to the participant's test ear with a headphone (HD-25‐1 II, Sennheiser, Ireland). The frequency response of the headphone was measured using a sound-level meter (System 824; Larson Davis, Provo, UT) and used to derive a SPL correction for ear-canal acoustics. The headphone was coupled to the sound level meter using a Larson Davis model AEC 100 coupler. Additionally, a correction for the acoustics of the pinna and ear canal was determined from measurements made using KEMAR (G.R.A.S. Sound and Vibration A/S, Denmark) and a sound-level meter. These two corrections were combined to derive a free field to eardrum correction function that was subsequently applied to the CLS measurements. Although this correction is not a true free-field correction (e.g., Shaw, 1965), it accounts for most of the frequency response-shaping propagation path of the stimulus, missing only the propagation from external loudspeaker to pinna. This correction facilitates comparison of our loudness measurements to other loudness measurements that were made with a free-field sound source. matlab software (Natick, MA) was used to control stimulus delivery and to record the responses of the participants.