Turntable Signal to Noise Ratio

[Primalsea]

How is this measured on a turntable ?
(I know how to calculate it from the measurements).

I guess you must have a test record and cartridge with known signal to noise ratios at a particular reference level. Then use them on a TT and measure the output and compare it to the test signal.

Now I know that tech specs often have no bearing on subjective sound quality. However whats confusing me is the S/N ratios being quoted by many TT manufactures. There should be a reference quoted for the test signal overwise the spec is meaningless. All S/N specs for turntables don't mention the reference signal. Is there a standard reference that I can't find or is this another example of the misleading info given out buy manufacturers.

I ask this because Clearaudio often brandish S/N ratios of 84db (with no reference) Pro-ject Audio TT's have much lower S/N ratios even for their best TT's, and again no reference. This means that it is quite possible that Pro-ject TT's could actaully have similar S/N ratios to Clear Audio TT's depending on the refernce used.

I know that many people won't find this post very interesting but I was hoping that there are some other sad people out there who might know the answer.