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HearTomorrow

Electroacoustics lab

Here is a collection of sound samples for audio test purposes. They are in standard "WAV" format, with a short descriptive text for each of it. All samples are ten seconds long, except as noted. Most can be concatenated if needed, since all are set to begin and end on zero-cross. A certain skill level in the electroacoustics field is recommended.

Note: If your sound card has digital processing options such as reverb, chorus, "3D-wide", or any equalizer, please make sure to disable it, as they would hinder proper operations.

White noise

has a frequency distribution of 1 (i.e. all components of equal intensity). As seen from the spectrograph, this corresponds to a "flat" response.

White noise

 

Pink noise

this is "1/f noise," with a frequency distribution of 1/f, or a 3dB per octave roll-off. It is generally considered the kind of noise most prevalent in nature.

Pink noise

 

Brown noise

this variety derives its name from "Brownian motion", and is the kind of noise associated with such "random walks." It has a frequency distribution of 1/(f^2), which is to say a roll-off of 6dB per octave.

Brown noise

 

Blue noise

this is, in a sense, the inverse of "pink" noise, with an increase of 3dB per octave. Intensity is proportional to f(requency).

Blue noise

 

Violet noise

this is the inverse of "brown" noise, with a pre-emphasis of 6dB per octave, or an intensity characteristic of f^2.

Violet noise

 

Linear Sweep

this starts with one second of 20Hz, followed by a fast "sync pulse" which might conceivably be useful for synchronizing a storage oscilloscope. Immediately thereafter, it sweeps linearly from 20Hz to 20kHz at a level of -3dB (relative to 0dB = 100% modulation). Total duration of the sweep is ten seconds.

Linear sweep

 

1/3 oktavesteps

this sample is useful for "manual" frequency response measurement. It has two-second samples of fixed tones from 20Hz to 20480Hz, spaced logarithmically in 1/3 octave increments, for a total of 31 samples. The actual frequencies are shown in the spectrogram.

1/3 octave steps

 

Square waves at four different frequencies: 10Hz, 100Hz, 1kHz e 7.35kHz (the 7.35kHz rate was chosen to avoid artifacts due to digital aliasing).

Burst tests - these are useful for checking amplifier transient response. All have a repetition rate of 10 bursts per second, so it would be useful to set your oscilloscope for a horizontal scan rate of 5Hz.

Burst Test 1

bursts of 100Hz sine waves, duration 0.04 seconds, interspersed with 0.06 seconds of silence.

Burst Test 2

bursts of 1000Hz sine waves, duration 0.02 seconds, interspersed with 0.08 seconds of silence.

Burst Test 3

bursts of 7350Hz sine waves, duration 0.01 seconds, interspersed with 0.09 seconds of silence. This "oddball" frequency was used to insure that each digital representation is identical, eliminating aliasing effects which would otherwise occur.

Intermodulation (SMPTE)

his contains 10 seconds of 60Hz at -3dB, superimposed on 7000Hz at -12dB, in compliance with the SMPTE/DIN standard for intermodulation distortion measurement for audio equipment. If you don't have a way of getting a spectrograph of your amplifier's response, this still might be useful in an auditory test. Both tones should be pure and clean, with no warbling or "edginess" to them, and no additional audible artifacts. Try it at different volume levels, you'll readily hear if your system has excessive IMD especially at high volume. The low note will become progressively brassier, and the high tone will begin to warble as IMD increases.

 Intermodulation (SMPTE)

Intermodulation (7350Hz)

essentially the same idea, except that the high tone is 7350Hz (an even sub-multiple of the 44100Hz sample rate) to prevent the possibility of aliasing artifacts affecting your measurements.

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