Christmas has just gone by, presents have been opened, and what do you find? A brand new LCD TV, or a swanky new stereo system that you can perch proudly in your living room. But before you can start enjoying your cool new AV gadgets to the fullest, let’s do a quick run through their specs. This way we will understand what they mean, and also what they don’t...

Audio Specs
Frequency Response
This is a basic spec but an important one. It applies both to amp and speaker. It’s a bit more vital for amps, as the sound needs to be amplified correctly for the speaker to do anything at all. It is measured in Hertz, actually a Hertz range. Where did this all this technical jargon come from, especially when everyone is in a party mood?

A typical frequency response curve showing levels for different frequencies

The human ear can hear only a range of available sound frequencies (20 Hz-20 KHz). Thus the amp should be able to reproduce the original song within this range, but that’s not all. If it was, all amps would sound the same, but they don’t, so it's clear the amps produce certain sound frequencies in slightly different amounts. Some amps have louder mid frequencies, while others have louder bass. In the frequency response rating a number in dB units (e.g. +/-3 dB) tells us that the sound might be louder (or softer) by an amount of 3 dB at certain parts of the response curve.

THD
THD (Total Harmonic Distortion) is another rating that says a lot in the fine print, though one can never really judge the actuality of this rating. It stands for Total Harmonic Distortion. As the name suggests, it talks about distortion: a bad word in Hi-Fi parlance. For the curious, harmonic distortion involves extra components in the output signal, that are not originally in your song. This extra material is not random, it appears in a proper structure at the output, in whole multiples of frequencies in your original song.

Another thing inherent in audio gear is noise. This noise is measured and given to you, and mostly the specification reads THD+N, which is a combined reading of all the unwanted stuff your amp produces. Lower is better: a figure of below 0.01% is required.

SNR
This is a detailed spec, the measurement of which varies among products. It stands for Signal to Noise ratio. What does it mean? It basically talks about how much noise is in your system, in an indirect way. Not to be confused with the N in the THD + N, SNR measures the noise level without any input, and compares that to a reference output level. The ratio between the two levels is the SNR. It is rated as a simple dB value; e.g. 90 dB is a common rating. The higher the better. Manufacturers are expected to mention their reference level for checking, but few do.

Sensitivity
This is a straightforward measurement. It’s the amount of volume the speaker can deliver, in terms of dB SPL (an acoustic unit to measure volume in open spaces) right in front of the speaker. The power is limited to one watt, and the distance is to one meter. The higher the value, the better, as that means the speaker can go louder with lesser rotation of the volume knob eastwards. In other words, less power is required to attain a certain level of music.

Output Power
Do I need to explain this? Just for the record, it is the maximum power an amp can deliver, and the maximum power a speaker can draw. It is measured in RMS Watts. There can be a huge number in the specs, though it must be known that on an average, home amps more or less operate with 1 watt. If you have high sensitivity speakers, 8 watts is more than enough for a bedroom.