The nature of the phonetic difference between the voiceless lenis consonants and the similarly voiceless fortis consonants is controversial. It is generally described as a difference in articulatory force, and occasionally as a difference in articulatory length; for the most part, it is assumed that one of these characteristics implies the other.Lenis and fortis here refers to a whole bunch of consonant pairs, written in IPA: /p-b/, /t-d/, /k-ɡ/, /s-z/, /ʃ-ʒ/. In any case, I have to learn how to properly say the voiced English consonants. I have started this training last year, most notably with my effort to make the word "fog" sound different from a four-letter-word and "bug" sound different from a colloquial unit of currency. I still have to train this a lot, but now I am faced with another problem: the IPA sounds /s-z/ in English are both written as "s" (except in zoo and some American spellings like "digitize", "monetize", "analyze"). Although this sound does not distinguish word pairs as often, it can still lead to non-understanding when pronounced wrongly. Furthermore, with an impeccable accent as a long-term goal, I would also like to distinguish /θ-ð/ which are both written as "th" in English. It's unvoiced in "thaw, think, earth, ..." and voiced in "they, the, this, ...". I will have to look up every word to find out; and then learn it again. Fortunately, as I start writing in Quikscript, I have an easy way to remember all those pronunciations.
PS: posts on Quikscript upcoming. ;-)