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More tracks to demonstrate the psychology of auditory perception
hidden_tone: This track demonstrates the phenomenon of "hidden bass". The first few seconds is a synthesised waveform composed of the 2nd, 3rd, 4th and 5th harmonics of a 440Hz fundamental; except that no fundamental is present! There follow several seconds of a 440Hz sinewave. And the track finishes with a repeat of the first waveform; harmonics only, no fundamental. Note how the perceived pitch of the sound doesn't change, the ear effectively "fills in" the missing fundamental.
hidden_bass: Similar to the previous track, but with a fundamental of 100Hz.
phase_deaf: This track consists of a 261 Hz tone with 50% third harmonic (783 Hz). In the first 5 seconds, the third harmonic has a zero phase relationship with the fundamental: in the second half the third harmonic has a 90 degree offset. Notice that the timbre is exactly the same. The ear is phase-deaf to this type of steady state sound; hence the reason why tone controls which affect phase response are tolerable in audio.
triangle: triangular waveform at 261 Hz fundamental.
inc_mod_index: Demonstrates the effect of increasing modulation index. The 440Hz tone is modulated by a modulation frequency of 330Hz with an increasing modulation depth. Note the brightening of the tone as modulation depth increases.
bell_1: A reversed and edited version of inc_mod_index; showing how a gradually decaying modulation index (coupled with the appropriate amplitude envelope) can be used to generate a sound wherein the harmonic complexity decays throughout the tone. The resulting composite tone is very bell-like.
bell_2: Delay effect added to a (slightly attenuated) bell_1.wav, to add realism to the bell sound.
bell_3: Bell_2.wav, used as a sample to generate a Westminster chime.
hammond: The first part of this track is a simple additive synthesis of squared sinewaves in the following proportions: fundamental x 100%, 2nd harmonic x 56%, 4th harmonic x 35%, 6th harmonic x 21% and 8th harmonic x 32%. Already, the sound has the characteristics of a Hammond organ. The classic tone-wheel Hammond organs produced reasonably high purity sinewaves; using squred sinewaves helps add the distortion which the amplifiers and keying circuits introduce. After 3 seconds a simple chorus effect is added to give the sound the simulation of the Hammond organ sound amplified and passed through a Leslie loudspeaker.
Unfortunately not all vocal performances can be captured in the hallowed halls of La Scala, Milan. So how might we capture the particular characteristic of an individual performance space? This is the aim of convolutional reverb.
There exists the interesting possibility that, if a very short pulse (known as an impulse function) is played over loudspeakers in an acoustic environment: and the resulting reflection pattern recorded with microphones and stored in a digital filter, that any signal - passed through the resulting filter - would assume the reverberation of the original performance space. Truly one could sing in La Scala! The next two tracks are intended to demonstrate the principle of convolutional reverberation.
reverb_signature: This is a recording of a short impulse, recorded in a church.
convolved_reverb: In this track, reverb_signature.wav is used as the impulse response and convolved with a short organ tone. The result is the reverb signature of the church "imprinted" on the organ tone.
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