I am going through Catford's Practical Introduction to Phonetics, experiments 31-32. After explaining how to produce voiced stops [b], [d], [g] by superimposing a closure upon the voiced air-stream, the author asks the reader to try producing their lengthened variants — [b b], [d d], [g g] by prolonging "the period of closure while keeping the voice going throughout" (p. 44). Catford then remarks that it may be difficult keep the voicing going long enough for lengthened voiced stops and offers a method of doing so by starting to lower the larynx at the moment when the closure is made.
My two questions are:
- I think I am struggling to do this correctly. Most of the times when I try to pronounce lengthened voiced stops as described above, I feel that the air goes through my nose as well, so the produced lengthened [b], for example, inevitably involves the humming sound of [m]. Are there any tricks to prevent the air from going to the nose, or is it impossible in this case?
- In the languages which have geminated voiced stops, are they pronounced by passing the air only through the oral cavity, without any voicing going through the nose?