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Ever wonder...
How it works: This CD contains precise, computer-calculated audio signals. Each sample is as mathematically perfect as the CD audio format allows. Left and right signals are identical in amplitude and phase, allowing you to check channel balance and phasing. Precise sinusoids check frequency response over a range of 5 to 20,480 Hz. White noise exercises the full spectrum uniformly. Precise square waves enable measurement of transient and phase response. Pure and mixed sinusoids at maximum amplitude enable distortion and inter-modulation measurements.
Signals are announced for easy identification. Most are on dedicated tracks, so they may be easily looped. They are also described by CD TEXT, and will appear on players that support this capability.
Precise measurements require instruments. An inexpensive sound pressure level meter can measure sound levels within your listening space. An inexpensive voltmeter can measure signal levels at speaker terminals, and at points farther back in the signal chain. For more sophisticated measurements, a precision microphone, oscilloscope, or spectrum analyzer (or a PC capable of these functions) is useful. However, the most important characteristics (such as smooth frequency response and centering) can be reasonably estimated by ear. For example, while listening to the 20 - 20,480 Hz frequency sweep (1 second per octave, 10 seconds total,) adjust your graphic equalizer so that there are no apparant peaks or drop-outs in volume. This will compensate for frequency characteristics of both your equipment and listening environment. (Don't be too disappointed if your ears fail to respond at the extremes of this range.)
Supplied with a copy of this How-To Article.
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Tracks |
Content |
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1 |
Introduction (announcement track)
The Precision Test Signals on this CD are suitable for accurate evaluation, calibration, and adjustment of frequency response, phase response, and distortion characteristics of audio systems. Each digital audio sample is computer calculated to the maximum accuracy supported by the CD-audio format. Left and right channel signals are identical in frequency and phase. Unless otherwise noted, all signals are recorded 6 dB below maximum level. |
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2 - 5 |
Quick Frequency Check Suite |
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3 |
10-Octave Sweep 20 Hz - 20.48 KHz at 1 octave/second sweep rate |
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4 |
Steady sinusoids at octave intervals within decade intervals: 20, 40, 80, 100, 200, 400, 800, 1000, 2000, 4000, 8000, 10000, 20000 Hz, 10 seconds each, announced, all on one track |
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6 - 84 |
Detailed Frequency Check Suite |
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6 - 79 |
Steady sinusoids at 1/3 octave intervals: 5, 6, 8, 10, 13, 16, 20, 25, 32, 40, 50, 63, 80, 101, 127, 160, 202, 254, 320, 403, 508, 640, 806, 1016, 1280, 1613, 2032, 2560, 3225, 4064, 5120, 6451, 8128, 10240, 12902, 16255, 20480 Hz Each frequency on separate 10 second track, following 4 second announcement track |
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81 |
12-Octave Sweep 5 Hz - 20.48 KHz at 1/5 octave/second sweep rate |
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83 |
Full-spectrum white noise, 1 minute track |
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85 - 95 |
Phase Response Suite |
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85 - 92 |
Square waves at decade intervals up to 1KHz 1, 10, 100, 1000 Each frequency on separate 10 second track, following 4 second announcement track |
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93 - 94 |
Square wave at 10% of CD-audio sampling rate, 4410 Hz 10 second track, following 4 second announcement track |
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96 - 99 |
Saturated Distortion Suite |
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97 |
1 KHz sinusoid at maximum level |
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99 |
50 Hz sinusoid at 90% of maximum level, mixed with 5 KHz sinusoid at 10% of maximum level |
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