Adrian, slew rate is one of the specs(damping factor is another)that the audio consumer doesn't have to worry about comparing between units he's considering for purchase. The reason is that the frequency response of the unit serves as a proxy for necessary slew rate. In order to reproduce 20KHz with a flat response and with low distortion an amplifier has to be able to respond to a signal moving 20,000 times a second quickly. The formula for calculating this at a certain power level is (6.28 x frequency x peak voltage)/1,000,000. For example, for 100 watts into 8ohms a peak voltage of about 40v is required, and the formula becomes (6.28 x 20,000 x 40)/1,000,000= 5.02 volts per microsecond. So, as long as the amplifier can change("slew")at a rate of 5.02 volts per microsecond, the 20KHz signal can be reproduced accurately at 100 watts. Typically, an octave higher response, i.e., 40KHz, is designed, which requires twice the slew rate, 10V/microsec. Since lab tests routinely show flat low distortion response to beyond 20KHz in even modest cost units, this establishes that the slew rate is adequate and not a matter of concern.
Of course, sometimes manufacturer hype(or naive audiophile belief)promotes much higher slew rates than required, with at least an implication that this would somehow make the sound "quicker". This is pure nonsense, and if a frequency was reproduced quicker than the Hz number, the correct term would be distortion. So, any number in the low double digits is fine for typical power levels, and specs showing rates of 50 or more which appear for some units aren't of real significance.
