Editor's Choice: Stereophile's Sampler & Test CD Tracks 17-19
This track consists of a steady tone with a frequency of 1kHz generated in the digital domain. Its level of -20dBFS—which is 20dB below the maximum peak level of a CD or laserdisc player—corresponds in a THX-specified system to an acoustic level of 85dB SPL. To compare preamplifiers, power amplifiers, or CD players/processors, measure the level of this tone with an AC voltmeter at the loudspeaker terminals, and adjust the volume control so that the meter reads 1V (1000mV). As long as each component being compared produces a measured level that's within 10mV of 1V (990-1010mV), volume differences will not confuse the auditioning.
 Dual-Mono Pink Noise
This and the next three tracks are intended to enable audiophiles to get a handle on how their systems and loudspeakers interface with their listening rooms—even if they don't have any test equipment.
The sound on track 18 is random noise with equal energy per musical octave, recorded in dual-mono. Called "pink" noise by engineers, it easily enables the listener to hear loudspeaker problems.
What you should hear: Pink noise ideally sounds like absolutely smooth rushing water with no band of frequencies sticking out any more than any other. It should not sound hollow or colored in any way, while the image of the noise should appear to come from a narrow point midway between the speakers. If the sound of this track fails to meet any of these criteria, then try sitting higher or lower, closer or farther away, or moving the speakers and/or nearby furniture.
 Chromatic Scale (left channel, then right channel)
All test CDs feature a conventional frequency sweep. Instead, I decided to include a musically relevant test signal. This track features sinewaves tuned to the frequencies of the modern equal-temperament scale, sweeping up in half-steps from the low C1 at 32.7Hz (on the space five ledger lines below the bass staff) to the high C8 at 4.186kHz (nine ledger lines above the treble staff) and back down again. Each note has a frequency equal to the frequency of the one below it multiplied by the 12th root of two.
The scale appears first in the right channel, then in the left, and, to aid identification of system resonant frequencies, the other channel in each case features the octave C notes played on a Sound Blaster synthesizer card set to its "Timpani" voice. Middle C, or C4—the note between the bass and treble staves—is identified with a double note, as is the very highest C. The marker Cs have the following frequencies: 32.7Hz, 65.4Hz, 130.8Hz, 261.6Hz (middle C), 523.25Hz, 1046.5Hz, 2093Hz, 4186Hz.
What you should hear: With small speakers, it's possible that you won't hear the lowest notes. Otherwise, the scale should sound even, without some notes sounding louder or softer than others (though in the bass, room problems will make this unlikely). If you do hear something wrong, note where it stands in relation to the marker "bonks" in the other channel. You'll then have a rough idea of the frequency range affected, and whether it's due to a room standing-wave (30-200Hz) or a loudspeaker crossover problem (1.5-4.5kHz).
With loudspeakers, play the scale and listen to the cabinet walls with a stethoscope (about $20 from any good pharmacy). You'll hear a cabinet resonance as an accentuation of the note. If the resonance is particularly severe when you pause the CD player while the affected note is playing, you might even hear it ringing on its own. If the cabinet has resonances but they don't lie at the frequencies of musical notes, it's possible that they'll have less of a deleterious effect on music.