Auditory scene A Diederich International University Bremen USC

Auditory scene A. Diederich– International University Bremen – USC – MMM – Spring 2005

– Music provides us with a complex, rapidly changing acoustic spectrum, often derived from the superposition of sounds from many different sources. – Our auditory system has the task of analyzing this spectrum as to reconstruct the originating sound events. 2 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Two mechanisms – The first is a fast, involuntary process of auditory grouping – The second involves using schemas to guide the grouping and listening process. Schemas are higher-level hypotheses or expectations based upon our knowledge of familiar sound. 3 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Grouping – Dimensions along which grouping principles operate: frequency, amplitude, temporal position, spatial location, timbre – Principles that govern grouping along these dimensions 4 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Principles of auditory grouping – – – – Similarity of timbre Similarity of pitch Temporal proximity Good continuation Location Onset and offset Experience 5 A. Diederich– International University Bremen – USC – MMM – Spring 2005

– The Gestalt approach to perceptual organization: How elements are grouped: Goldstein, pp. 148 – 156 – Auditory scene analysis: Identifying sound sources: Goldstein, pp. 395 – 401 – CWE, 245 – 247, 411 – 417 – Shepard, R. Stream segregation and ambiguity in audition. In: Cook, Chapter 10 – Deutsch, D. Grouping mechanisms in music. In: D. Deutsch (Ed), The Psychology of Music, (1999), Chapter 9 6 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of similarity Similar things appear to be grouped together. 7 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of similarity 8 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of similarity 9 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of similarity 10 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Similarity of timbre – Sounds that have the same timbre are often produced by the same source. – This principle means that we tend to group stimuli that sound similar together. – If pairs are alternately similar and dissimilar in timbre, they will group by similarity. 11 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Similarity of timbre Auditory stream segregation A. Diederich– International University Bremen – USC – MMM – Spring 2005

Example Grouping by timbral similarity: trumpet tones alternating with a vocal tone and a steel drum sound. Track 31 13 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Similarity of pitch – Sounds with similar frequencies are often produced by the same source. – Imagine tones with different pitch. Those tones close in pitch will become grouped by similarity. 14 A. Diederich– International University Bremen – USC – MMM – Spring 2005

A. Diederich– International University Bremen – USC – MMM – Spring 2005

Example 1. 2. 3. 4. 5. 6. 7. 8. High and low pitch played in succession; easy to follow as single line High-low-high pattern repeated ever faster until there are two streams of pitch Slow alternation between a minor second apart. Note that it is easy to think of the sound as a single line Same as 3. , but the interval is wider Same interval as 3. , but faster Same interval as 4. , but faster Same as 3. , even faster. Do you here one or two lines? Same as 4. , even faster. Do you here one or two lines? Track 32 16 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Composers in the Baroque period (1600 – 1750) knew that if a single instrument plays notes that alternate rapidly between high and low tones, with the high notes perceived as being played by one instrument and the low notes as being played by another. This effect, which has been called implied polyphony or compound melodic line, is an example of auditory stream segregation. 17 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Example of Gestalt grouping and stream segregation Track 37 18 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Similarity of pitch J. S. Bach, Cello Suite I, Prelude A. Diederich– International University Bremen – USC – MMM – Spring 2005 19

Law of proximity or nearness Things that are near to each other appear to be grouped together. 20 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of proximity or nearness 21 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of proximity or nearness 22 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Left: Competition between grouping by proximity (columns) and grouping by similarity ( rows) Right: Demonstration of active grouping when multiple possibility are available 23 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Temporal proximity – Sounds that occur in rapid progression tend to be produced by the same source. – Grouping a set of tones so that some are closer together than others are perceived as belonging together. – If steps are large and rapid (e. g. , on a diatonic scale), melodies are not perceived as a stream but segregate into separate entities. 24 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Example Yodeling: The singer alternates between the head and chest voice modes of production, and the leaps are large and rapid. The high note and low notes of yodeling are often perceived as two separate streams. Track 33 25 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Interleaving two melodies – Another example that illustrates this phenomenon involves interleaving two melodies so that the notes of each melody alternate. – If the relative range of the melodies is such that the interleaved patterns contain small leaps, the individual melodies are not recognized. – As one of the melodies are transposed so that it is farther and farther from each other, a point it reached when both melodies are recognized. – The connection from one to the next is a function of proximity. 26 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Overlapped melodies cannot be separated even though they alternate in time. Separating in pitch allows the two melodies to be easily identified. Different timbre or volume 27 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Example 1. Melodies just seen 2. Same as in 1. , increasing distance between melodies each time 3. Separation by volume 4. Separation by timbre 5. Two new melodies, increasing distance 6. Separation by volume Track 34 7. Separation by timbre 28 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of good continuation Points that, when connected, result in straight or smoothly curving lines are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path. 29 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Law of good continuation 30 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Good continuation – Sounds that stay constant or that change smoothly are often produced by the same source. – Sound stimuli with the same frequency or smoothly changing frequencies are perceived as continuous even if they are interrupted by another stimulus. 31 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Good continuation a) Albinez b) Perceived as two separate streams 32 A. Diederich– International University Bremen – USC – MMM – Spring 2005

33 A. Diederich– International University Bremen – USC – MMM – Spring 2005

Example 1. Sinusoid going up and down in pitch with pauses at the top 2. Gaps in previous example are filled with noise. Now the sine wave sounds continuous, but is just obscured by the noise burst. 3. Musical example with gaps 4. Musical example with gaps filled by noise. Track 5 34 A. Diederich– International University Bremen – USC – MMM – Spring 2005

– http: //www. ece. uvic. ca/~aupward/p/demos. htm – http: //www. psych. mcgill. ca/labs/auditory/bregmancd. html 35 A. Diederich– International University Bremen – USC – MMM – Spring 2005