Hot wired: Powerful audio dynamics

When I researched the resurgence of the turntable for an earlier Hot wired column, the debate about diminishing dynamics in recorded music came up.

Vinyl, you see, is still reckoned by its zealots to provide a much greater range of dynamics than digital recordings like CDs.

Dynamic range is an expression of relative loudness - the difference between the loud bits and the quieter bits of a song. Of course, if you turn the big knob up from three to 10 everything will sound louder - that's simply volume. Compare the noise level of a solo flute with a full orchestral blast, or a finger-picked guitar note against a power chord thrash and that's dynamics.

Disgruntled TV viewers have long argued that broadcasters turn the volume up for ads. I'm with them - why else do you sleep through programmes but always wake up for the ads? The usual disclaimer: "No we don't, the ads simply have different dynamics to TV programme soundtracks."

Unfortunately, this is plausible. Modern broadcast and recording techniques allow engineers to easily bulk up sound at the push of a button. Compression and limiting are the two main electronic tools used to alter dynamics.

By reducing the overall dynamic range (loud to soft) as compression does, making more of the sound close to the maximum level, the listener can be fooled into thinking it is all louder. TV and radio ads can exploit this because of their brevity. Programmes can't because they need to tell stories with quiet conversations through to explosions.

Radio stations are particularly prone to messing with dynamic ranges. They need to sound good on portable radios and car stereos, as loud as any other station on the dial and need to minimise quiet moments. That's why a song on a CD can sound different when played on your car radio. Recording engineers increasingly do special radio mixes which take account of how radio compression will affect the dynamics of songs.

Popcorn, the back row and the big screen aside, one of the thrills of going to the movies is that impressively huge sound. You can hear whispered dialogue clearly and car chases are plenty loud enough, yet the resulting explosions are still hair-raising. The same film re-engineered for TV will have its soundtrack dynamically compressed to take into account the typically poor TV speakers and the noisier home environment.

Wide dynamic range is something to aspire to in your own hi-fi or home-entertainment set up. It's one thing to be impressed by the impact of a system when it is running near full volume (a typical sales trick), and quite another to get a real sense of the music or movie soundtrack at relatively low, normal listening levels.