Emma SAHS HW3B LAB 2023 (1)

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Apr 3, 2024

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Emma Connolly CMD304 HW3B Psychoacoustics Demonstrations 1. Demo #6. Download the audio files (17 and 18) from Brightspace (or click the link for Demo 6 and then click the links for the files) and play them. Use a good pair of stereo headphones. Adjust the sound level so you can barely hear the calibration tone. Record the number of steps you hear at each frequency for each trial: Frequency (Hz) Trial 1 Trial 2 125 250 500 1,000 2,000 4,000 8,000 For which frequencies is your hearing more sensitive (more steps heard)? For which frequencies is it less sensitive (fewer steps heard)? Explain these results in terms of what you know about the threshold of audibility curve. Also, how is this related to the properties of the middle ear? The sensitivity of human hearing to different frequencies is reflected in the threshold of audibility curve, with height and sensitivity in the mid frequency range and decrease sensitivity at very low and very high frequencies. These differences in sensitivity are influenced by the mechanical properties of middle ear, which affect its ability to transmit sound energy to the colia across the frequency spectrum. 2. Demo 7. Loudness scaling. Download the audio files (19 and 20) from Brightspace (or click the link for Demo 7 and then click the links for the files) and play them. Use a decent pair of stereo headphones. Listen to the reference sample and the softest and loudest sounds. Next, you will hear 20 pairs of stimuli. In each case, the first is the reference sound and the second is the test sound. Rate the loudness of the test sound (second sound) in each pair relative to the reference sound (first sound in each pair). Use the following scale: The reference sound has a value of 100. If the test sound seems twice as loud, your rating is 200; if it seems one-tenth as loud, your rating is 10, and so on. Sound number Rating relative to a reference value

Emma Connolly of 100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Download the attached spreadsheet, which includes mean data from a group of students. The mean data are in column C. In column D, you will enter your individual data. Each sound level was tested two or three times. Column E tells you which data to average for each sound level. After entering your averaged individual data in column C, highlight the data in columns B, C, and D (B2 through D10) and insert a scatter chart. Use a line for the data in column C and points for Column D. This will show you how close our individual ratings were to the mean for a group, in addition to showing you the overall trend of how loudness scaled with level. Explain the graph. Try to estimate how much of a level change results in a doubling of loudness. How does it relate to the “rule of thumb” of 10 dB per doubling discussed in class? Please upload the spreadsheet and graph along with the write-up. 3. Demo 37. Binaural Lateralization

Emma Connolly Download the audio files (72-74) from Brightspace (or click the link for Demo 37 and then click the links for the files) and play them. Use a decent pair of stereo headphones. Listen to the tracks and record your observations: a. 500 Hz tone and 2,000 Hz tone with changing phases: Did the sound appear to switch from one ear to the other as the timing(phase) was changed? If so, was this observed at 500 Hz, 2,000 Hz, or both? Explain your results based on what you know about localization based on interaural time/phase differences. The sound did not appear to switch from one ear to the other as the timing (phase) was changed. While there might be some subtle changes in perceived location as the timing of the 500 Hz tone is changed, the effects mighe not be as pronounced as it would be higher-frequency tones where interaural phase difference plays a more significant role. Interaural phase differences may become more critical in the 2,000 Hz tone because it is a higher frequency. You may observe shifts in perceived location. The brain interprets these phase differences are changes in direction of the sound source. b. As the clicks were presented to the left and right ears with different time differences, what did you observe? Explain your results based on what you know about localization based on interaural time/phase differences. As the clicks were presented to the left and right ears with different time differences, I observed that there were shifts in the perceived location of the sound source. This is due to the brain’s ability to use interaural time or phase differences to localize sound in space. c. 250 Hz tone and 4,000 Hz tone with changing intensities: Did the sound appear to switch from one ear to the other as the intensity at the two ears was changed? If so, was this observed at 250 Hz, 4,000 Hz, or both? Explain your results based on what you know about localization based on interaural intensity differences. The sound did appear to switch from one ear to the other as the intensity of the two ears. This supports “interaural level difference” which refers to the difference in intensity between the ears. It is a crucial cue for sound localization, especially for frequencies above 1,500-2,000 Hz. This was not as pronounced at 250 Hz because it falls within the range where interaural time differences (ITD) are more critical for localization. frequencies are easier to determined. On the other hand, 4,000 Hz where the wavelength is shorter and interaural time difference cues are less effective, the interaural intensity difference cues are more critical. This means that you are more likely to observe the location shifting from one ear to the other as the intensity at the two ear is changed. As the intensities change, the perceived location of the sound can switch between ears.

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Emma Connolly Demo 4. Masking Level Differences This is mostly for “culture,” to illustrate an interesting phenomenon, the binaural masking level difference. However, notice that your threshold for the tone alone is lower than the threshold measured when the masking noise is added. This is the general effect of masking. When masking noise with a specific phase relationship is added, we can hear the tone better! This is the masking level difference. We get a small amount of this benefit when listening to signals in real-world noisy environments. Download the audio files (75-79) from Brightspace (or click the link for Demo 4 and then click the links for the files) and play them. Use a decent pair of stereo headphones. In these tracks, a tone of 500 Hz is presented in different binaural masking conditions. Record the number of steps you hear at each frequency for each trial: Condition Trial 1 Trial 2 Tone alone in left ear Tone with masking noise in left ear Tone in left ear with masking noise in both ears Tone in both ears with masking noise in both ears Tone in both ears but 180 degrees out of phase, masking noise in both ears Try to explain these results. Why does hearing for the tone in one ear improve when the noise is added to both ears? (hint: having noise in both ears makes the sound seem to come from the midpoint between the two ears). For the binaural presentations, what does the phase change of the tone allow us to do? Hearing for the tone in one ear improves when the noise is added to both ears because…. For binaural presentations, the phase change of the tone allows us to… Demo 5. Auditory illusion Download and play the audio file (80) from Brightspace (or click the link for Demo 39 and then click the to play the file). Use a decent pair of stereo headphones. As the tone pairs are presented, in which ear do you hear the high tones? In which ear do you hear the lower tones? Are you right- handed or left-handed? As the tone pairs are presented, the ear that I hear the high notes in is… The ear that I hear the lower notes in is… I am right handed.

Emma Connolly Apparently, the high tones are usually perceived as being in the ear that “feeds” the dominant hemisphere. If you hear the high tones in the right ear, your left hemisphere is dominant. Most right-handed individuals will hear the high tones in the right ear. About half of all left-handed individuals hear the high tones in the left ear, half in the right ear. (I am left-handed, and I heard the high tones in my left ear).

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