Halcro.

I think that the numbers and
green graph are useful provided their limitations are taken into account.

Mean frequency....

This is a good
number to have. We are looking for 3150Hz, so nice and close to this is desirable.

Raw frequency…

Max deviation. (relative )
This is the max percentage deviation, negative and positive, from the mean
frequency. Ideally the two numbers should be the same

Max deviation (absolute) This
is the max frequency deviation, negative and positive from the mean frequency. Ideally
the two numbers should be the same.

What the deviation numbers do
not show is the variation between the deviation of individual positive and negative
swings. They all should be the same, (constant amplitude) and for this information we need to refer to the
yellow graph.

Lowpass-filtered Frequency.....

This data taken from the
green trace. The limitation here is that this trace is heavily filtered version
of the yellow trace. And it is very inconsistent from test to test.

Look at the 1000R yellow trace
and compare this with the TT-101 yellow trace. There is an enormous difference
yet, post filtering they yield very similar green traces

I have run sequential tests
on my SP10 Mk 3 and got Low pass -0.01%/+0.01% followed by -0.02%/ +0.03%. I have outlined some of the reasons for this inconsistency. As I said earlier, below a certain percentage, these figures aren't robust.

Obviously we do not want to
see any standout perturbations in the green trace and in this way it can be
very useful.

My point is that this data is
derived from the yellow trace which is taken from the cartridge output. After all, it is the cartridge’s output that we listen to. To really see how the TT is behaving in fine
detail, we need to analyse the yellow trace from the perspective of
what a perfectly speed stable TT would look like. A clean sine wave, symmetrically centred around 3150hz with a constant amplitude for each cycle. As we can see, advances in
technology have clearly improved the situation.

The subsonic speed resonance in
the TT-101 can be seen as periodic cycling every 5 revolutions. If you look at
the first traces you posted (yellow) , you will see a positive peak just after 5 seconds. This
peak appears again just after14 and 23 seconds. The smaller positive and negative excursions in between these peaks follow the same pattern with their 9 second spaced partners. There is a recurring pattern to the shape
of this waveform with a period of 9 seconds.

Cheers,