With the Zenith-DBX TV stereo sound system, you could pick up some pumping artefacts when listening to stereo sound broadcast on decent equipment, including a good outboard TV tuner with split sound. But it wasn’t overwhelmingly bad, I think because only the difference channel was companded. On the mono SAP channel, the pumping was fairly obvious. But I can’t say that I’m a fan of the DBX system generally.
Re the use of the LSB only in decoding the Zenith-GE system, we’d need to find the original report about the tuner so-equipped to ascertain just what claims were made, although I am certain that lower noise was one of them.
With regular AM synchronously demodulated, it is clear that using one sideband alone confers a noise penalty as compared with using both, which is why for example decent synchronous HF programme-content listening receivers gave you a choice between LSB, USB and DSB. DSB also gave you some benefit from sideband diversity when there was selective fading. I am relying on distant recall, but I think that the argument used to support LSB-only subcarrier demodulation with the Zenith-GE system was that because of the triangular noise spectrum of FM, the USB was a lot noisier than the LSB, such that the loss of S/N due to the loss of one sideband was more than offset by the elimination of the noisy USB. Whether that proposition would hold up to quantitative analysis, I don’t know.
Using just the subcarrier LSB for transmission was proposed in the late 1950s, including by Siemens and Philco. This was mentioned in BBC Monograph #29 of 1960 April (
http://downloads.bbc.co.uk/rd/pubs/a...nograph_29.pdf), with comparative S/N numbers; it was slightly better than DSB. The Siemens proposal was also mentioned in BBC RDR 1962-49 (
http://downloads.bbc.co.uk/rd/pubs/reports/1962-49.pdf).
Cheers,