The following sounds demonstrate the auditory perceptual phenomenon known as dichotic pitch (also known as binaural pitch). Dichotic pitch is a pitch perception produced by two binaurally fused noise sequences, neither of which alone contain any cues to pitch. (For more on dichotic pitch, see dichotic pitch explained and Time-Shift Dichotic Pitch. My matlab code for generating dichotic pitch is available.)

These demonstrations require stereo for the dichotic pitches to be perceived. They are best listened to with headphones at a comfortable listening volume (lower volume is better). Lowering the bass and treble may also facilitate the perceptions. To hear the sounds, click on either the AIFF or WAV format download button (WAV is best for Windows).

Demo 1 & Demo 2: introduce dichotic pitch by initially presenting monaually audible pitches. The signal-to-background ratio (SBR- see dichotic pitch explained for more details) is gradually adjusted down into the true dichotic pitch range (SBR <= 1). You can use these two demos to estimate your dichotic pitch detection threshold. These demos are similar to the stimuli used in our 1998 NeuroReport paper (see abstract).

Demo 3 is the place to go if your bandwidth and/or time is limited and you just want to hear a neat dichotic pitch stimulus. It presents dichotic pitches that move about in virtural auditory space.

Demo 4 plays a melody with dichotic pitch.

Demo 5 plays musical scales over the 3 to 4 octave existence region of dichotic pitch.

Demo 1: Melody Lateralization

These sounds are similar to the stimuli used in the melody localization task described in our 1998 NeuroReport paper (see abstract).

This sound file includes 10 presentations of a 4-note melodic signal at decreasing signal-to-background ratios (SBRs). The SBRs start at 4 and decrease in 4 dB steps (the values are presented in the table below). The background noise has an interaural time difference (ITD) of 0, so it should be perceived to be in the middle. The melodic signal ITD is randomly set to lead either the left or the right ear by 0.6 ms, so it will be perceived to be either to the left or to the right of the central background noise.

You can estimate your SBR threshold by counting how many of the 4-note melodies you can confidently lateralize to the left or right. For example, if you hear and can lateralize the first 5, but not the 6th, then your threshold is between 0.63 and 0.4. If your threshold is at or below 1 (in the yellow zone on the table below), then you can hear true dichotic pitch.

demo 1 (AIFF format)

demo 1 (WAV format)

Demo 2: Pitch Identification

These sounds are similar to the stimuli used in the pitch identification task described in our 1998 NeuroReport paper.

This sound file includes 10 presentations of a 3-note signal at decreasing SBRs (same values as demo 1; see table above). The signal ITD is fixed to lead one ear by 0.6 ms, so it will be perceived to be to one side of the central background noise. However, each 3-note sequence is either rising (400 Hz, 500 Hz, 600 Hz) or falling (600 Hz, 500 Hz, 400 Hz). You must determine which it is.

You can estimate your threshold by counting how many of these 3-note sequences you can confidently identify as rising or falling. For example, if you can identify only the first 6, then your threshold is between 0.4 and 0.25. As in the first demo, if your threshold is at or below 1, then you can hear true dichotic pitch. Unfortunately, if your threshold is not below 1, you probably will not hear the remaining demonstrations.

demo 2 (108 KB; 5 KHz 8-bit stereo AIFF file)
demo 2 (108 KB; 5 KHz 8-bit stereo WAV file)

Demo 3: Moving Tones

This sequence begins with 2 monaurally audible tones to orient you to the dichotic pitches which follow. The signal and background ITDs change over time, so that each may appear to move laterally through your head.

These moving tones are true dichotic pitch, thus you will not hear them if you listen with only one ear. Some individuals may lack the ability to extract dichotic pitch. If you don't hear the moving tones, see demo 1 or demo 2 to detemine your dichotic pitch threshold. (It's also possible that your computer isn't playing the sounds in stereo.)

demo 3 (AIFF format) (92 KB; 5 KHz 8-bit stereo AIFF file)
demo 3 (WAV format) (92 KB; 5 KHz 8-bit stereo WAV file)

Demo 4: Name That Tune

All notes are true dichotic pitch (SBR = 1). Can you identify the melody? Try listening with only one ear first. It should be impossible to hear the melody when you listen with only one ear. Musical arrangement by Matt Tata and Bob Dougherty.

demo 4 (AIFF format) (170 KB; 5 KHz 8-bit stereo AIFF file)
demo 4 (WAV format) (170 KB; 5 KHz 8-bit stereo WAV file)

Demo 5: Scales

All notes are true dichotic pitch (SBR = 1). These major scales span the existence region of dichotic pitch. The scales start at C (65 Hz) and run through 4 octaves to C (1047 Hz). The notes include harmonics (this facilitates the dichotic pitch percept).

demo 5 (AIFF format) (180 KB; 5 KHz 8-bit stereo AIFF file)
demo 5 (WAV format) (180 KB; 5 KHz 8-bit stereo WAV file)

Copyright policy. Contact: bobd@stanford.edu. Last modified 2011-Nov-07 17:40 GMT.