The fascinating thing is the same applied for female voices in the same era in the UK too. I had always thought it was some artefact of the awful posh received

The fascinating thing is the same applied for female voices in the same era in the UK too. I had always thought it was some artefact of the awful posh received pronunciation everyone was expected to adopt going through school. If you listen to pre-war newsreels or movies you'll get the same shrill female tones. Hearing Australian from then is similar, though sounds much like UK RP, with a more gentle hint of "Strine" than you'd expect today. Yet anyone who's been around long enough will have probably dropped pitch over the years. Listen to any wartime or pre war famous women speaking and hear them twenty or thirty years later, e.g. the Queen, Vera Lynn, not only has the stuck up constricted accent gone, but the pitch has dropped markedly too.