Technical
How Isostase actually measures platter speed
Regulating a turntable's speed first requires measuring it. And the measurement that matters is not the motor's but the platter's: the platter is what drives the record.
Measuring the platter, not the motor
Knowing the frequency sent to the motor does not tell you how fast the platter is actually turning. In between sits the belt, which can slip slightly, and a load that varies: the stylus drags on the record more or less depending on the groove modulation, and bearing friction changes with temperature.
Isostase therefore measures the platter's rotation directly, with a contactless optical sensor: a target on the platter passes in front of the sensor on every revolution. Nothing touches the platter, nothing slows it down.
A time measurement, referenced to quartz
The principle is simple: measure very precisely how long the platter takes to complete one revolution. At 33⅓ RPM, a revolution lasts 1.8 seconds; at 45 RPM, 1.33 seconds.
That time is counted by the microcontroller's clock, itself calibrated against a quartz reference. The resulting precision is considerable: to give an order of magnitude, an error of one microsecond over a 1.8-second revolution represents barely half a millionth, a deviation far finer than anything the ear or a stroboscope disc can perceive.
What a once-per-revolution measurement reveals
- The exact average speed, revolution after revolution, to correct any speed error.
- Slow drift: warming up, an ageing belt, changes in load.
- Belt slip, by comparing the platter's actual speed with the speed imposed on the motor.
- Revolution-to-revolution variations, which feed the live wow and flutter estimate and the "ready to listen" indicator.
It is also at this pace, once per revolution, that the regulation corrects the speed. This measured pace is deliberate: with a heavy platter, gentle and regular correction avoids introducing speed variations of its own.
Its limits, in full transparency
With a single target, Isostase sees the platter once per revolution. Whatever happens within a revolution escapes it: a fast speed variation, for example one caused by the rotation of the motor pulley, is averaged over the revolution.
That is why the Isostase wow and flutter reading is a diagnostic indicator, not a standardised measurement. A DIN or IEC measurement uses a test record cut at 3150 Hz and a dedicated analyser, which also capture fast variations.
More targets spread around the revolution would make it possible to follow those finer variations: this is a development Olydyne is currently studying.
In short
The Isostase measurement is a direct, contactless, quartz-referenced measurement of the platter's actual speed. It is highly accurate on average speed and drift, and it is what makes closed-loop regulation, belt monitoring and the wow and flutter estimate possible.