Turntable tests

Nottingham Analogue Hyperspace belt drive turntable – superb speed stability.

SPEED STABILITY

WHAT IT TELLS US

Speed stability is measured using an old term: ‘wow and flutter’. A turntable rotates at 33.3 rpm (revolutions per minute), so it manages 0.55 revs per second and this is its basic rotational frequency. In practice speed drifts either slowly or quickly, in random or cyclic fashion, depending upon the design and quality of execution.

Speed drift is the basic effect that gives rise to wow (low rate drift) and flutter (high rate drift). Drift is usually understood as occurring below 1Hz, wow from 1Hz to 10Hz, and flutter from 10Hz upward. Where there is no drift, or very slow drift, there is virtually no wow or flutter, a property of good Direct Drives and very high quality belt drives with heavy platters.

Drift brings a sense of uncertainty to pitch, in extreme form making music sound ‘drunken’. Wow is more a discrete effect, like a regular warbling of pitch for example. Flutter was a problem with tape machines in particular and ‘dirtied’ notes, robbing them of purity. All three effects frequency modulate music and introduce associated sidebands.

Technics SL-1200 MkII Direct Drive turntable – very low basic speed drift.

HOW WE MEASURE IT

We measure speed accuracy, wow and flutter using DIN 45 465 test disc cut with a 3150Hz steady tone. It has a locked outside groove that allows the disc to be carefully and accurately centred, vital if disc eccentricity is not to contribute to cyclic drift at 0.55Hz. With the disc centred it is possible to measure down to around 0.06% unweighted wow, sufficient to identify the performance of top quality turntables.

Our results, from an Audiomatica ‘Clio’ test set run on a dedicated computer, show speed accuracy as the replay frequency of the test tone, unweighted wow and weighted wow, as well as flutter.