Is there a reason golden age DD turntables became golden age? Or conversely, why did the high-end move to belt-drive?
I think there is.
Fundamentally, golden age DD tables employed a PLL (phased-locked loop) to stabilize rotational velocity to a very accurate degree. The problem herein is that the frequency response of this negative feedback loop (that's what a PLL is) is right in the middle of the audio band, sitting on top of vocals. Yeah. So for every disturbance or increase in stylus drag, there is a corresponding error term which gets amplified a drives a proportional (PID actually) response in the motor to compensate, adding it's own signature.
I'm pretty sure Fremer pointed this out a long time ago.
A DD may have an easy time hitting 33.3333 RPM long term average, but short term in-audio-band response may become audible and annoying. In short, that's why a decent belt-driven table is more relaxing and less fatiguing over the long term.
Thoughts?
I think there is.
Fundamentally, golden age DD tables employed a PLL (phased-locked loop) to stabilize rotational velocity to a very accurate degree. The problem herein is that the frequency response of this negative feedback loop (that's what a PLL is) is right in the middle of the audio band, sitting on top of vocals. Yeah. So for every disturbance or increase in stylus drag, there is a corresponding error term which gets amplified a drives a proportional (PID actually) response in the motor to compensate, adding it's own signature.
I'm pretty sure Fremer pointed this out a long time ago.
A DD may have an easy time hitting 33.3333 RPM long term average, but short term in-audio-band response may become audible and annoying. In short, that's why a decent belt-driven table is more relaxing and less fatiguing over the long term.
Thoughts?