The frequency response curves seen on our RMAA generated graphs are often used to indicate the accuracy of amplifiers and speakers in reproducing audio. Good frequency response does not guarantee a specific fidelity, but only indicates that a piece of equipment meets the basic frequency response requirements. As an example, a high fidelity amplifier may be said to have a frequency response of 20 Hz - 20,000 Hz ±1 dB. This means that the system amplifies all bands from 20 Hz to 20,000 Hz with a maximum positive or negative deviation from the straight line of only 1 dB. Larger deviations below 40 Hz or above 15 kHz are OK, since the human ear is unable to perceive those sounds. Here lower absolute numbers mean the handset treats all sounds equally; it won't impose its will on the music but will allow you to hear the music as it was recorded, which is what a good piece of audio equipment should do.

The noise levels are the next important aspect of sound reproduction. As seen in our tests, noise is usually measured in relation to the signal levels, otherwise known as the signal-to-noise ratio. In less technical terms the signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise ('background' meaning unwanted interferences created by the equipment). So the higher the signal-to-noise ratio, the less obtrusive the background noise, hence the reproducing equipment is of a higher quality.

The dynamic range is another important factor. The human sense of hearing has a very high dynamic range. A person is capable of hearing anything from a quiet murmur in a soundproofed room to the sound of the loudest rock concert. A difference like this can be up to 100dB. A person however cannot perform these feats of perception at both extremes of the scale simultaneously - you cannot hear a whisper in a noisy street for example. Nevertheless, a good quality audio reproduction system should be able to reproduce accurately both the quiet sounds and the loud at the same time. Audio engineers often use the term dynamic range to describe the ratio of the loudest possible undistorted sound to the quietest or to the noise level, say of a microphone or loudspeaker. This dynamic range of an audio device is also sometimes referred to as the dynamic window. To mathematically determine a dynamic range you must take the difference between the ceiling and the noise floor of an audio device. For example, if the ceiling of a device is 10 dB and the floor is 3 dB then the dynamic range is 7 dB, since 10 - 3 = 7. So the larger the dynamic range (or otherwise the dynamic window), the better the device performs at reproducing quiet and loud sounds simultaneously.

The total harmonic distortion (THD) and the intermodulation distortion (IMD) might be the next items you will notice on our measurement results. By the name you know they are a measure of the unwanted altering of the original signals. Distortion is the name given to anything that alters a pure input signal in any way other than changing its magnitude. So, as you might have guessed it, the lower the number, the better the sound reproduction.

The stereo crosstalk is another thing of importance that we measure in our tests. Crosstalk measurement is made to determine the amount of signal leaking across from one channel to another or in purely non-technical terms it measures how good the stereo is. So, the higher the absolute value, the better the stereo.