One of the first pronunciation difficulties that a student encounters when learning French is that various written consonants are actually “silent”, particularly on the ends of words. So for example, the words beau and chaud actually rhyme in French, even though the second of these ends in a written “d” while the first ends in no written consonant at all.
But there is an additional difficulty to mastering the pronunciation of French consonants. Even when they are actually pronounced, various consonant sounds which you initially expect to be the “same sound” as their English counterpart are in fact subtly different in French. You’d be forgiven for thinking that, say, a “d” sound is a “d” sound whatever the language, so that so long as it is pronounced in the first place, a “d” sound in French is the same as a “d” sound in English. Unfortunately, this turns out not to be the case and indeed assuming it to be the case can lead to communication difficulties.
Both English and French (and various other languages) share various consonants, termed stops, that come in pairs: “p”/”b”, “t”/”d” and “k”/”g”. These consonants are referred to as stops because in pronouncing them you… stop… the air flowing through the mouth (with the lips in the case of the first pair, and with part of the tongue against the roof of the mouth in the second and third). The two stops making up each pair (e.g. “p” versus “b”) differ in terms of vocal cord vibration: loosely speaking, the first of each pair is “voiceless” (lacking vocal cord vibration) whereas the second is “voiced” (having vocal cord vibration). As a side note, we should mention that their are potentially other pairs of stops across languages as a whole, but these ones are common to French and English.
So far, so good: the loose descriptions that we have just given of these six consonants apply to both English and French. But the devil is in the detail. For the reasons we’ll see in a minute, an English speaker’s voiceless stops are a little bit “more voiceless” than those of a French speaker, while the French speaker’s voiced stops are a little bit “more voiced”.
When a French speaker pronounces their version of these consonants, their behaviour follows the description above more or less as you might expect. Just as they bring their lips together to make a “p” sound, more or less simultaneously their vocal cords stop vibrating. And likewise, as they open their lips again, the vocal cords start vibrating more or less at the same time (provided, of course, there is a following sound such as a vowel that requires them to vibrate!). Conversely, when a French person pronounces a “b” sound (the “voiced” counterpart of the “p” sound, remember) they aim to keep the vocal cords vibrating right the way through. So when applied to a French speaker’s stops, “voiced” and “voiceless” really do describe whether or not their is vocal cord vibration while the sound or airflow is actually stopped.
On the other hand, the behaviour of a native English speaker is slightly different. When they pronounce a “p” sound, not only do their vocal cords stop vibrating while the lips are together, but when the lips are opened again and the air “released”, the native English speaker generally “forces” a small extra breath of air out. This “breath of air” is often termed aspiration and has the effect of delaying the onset of vocal cord vibration because of the increased air pressure flowing through the larynx. On the other hand, when an English speaker pronounces a so-called “voiced” stop such as a “b”, in reality they still allow the vocal cords to stop vibrating while the lips are closed, but instead differentiate from the voiceless stop by avoiding the aspiration.
(The eagle-eyed will note that the descriptions we give here apply specifically to stops at the beginning of a syllable. We focus here on voicing at the beginning of a syllable, but there are of course other differences in the pronunciation of these stops between French and English.)
Now look at these descriptions again closely: we said that in a French “p” sound, the vocal cords stop vibrating while the lips are closed. And in an English “b” sound, the vocal cords also stop vibrating. What this means is that an English “b” sound is actually very similar to a French “p” sound! A similar process applies to the other pairs “t”/”d” and “k”/”g”, so that in many cases, an English “d” is actually similar to a French “t” and an English “g” similar to a French “k”. Needless to say, this is one pronunciation detail that can potentially lead to confusion!
So what can you do in practice to pronounce these stops in a way that will avoid confusion to a French speaker? Luckily, we do have one starting point in English. It turns out that after a “s” sound at the beginning of an English word (as in sport, steak, skate/school etc), “p”, “t” and “k” are much more similar to their French counterparts. So to say the French word porte, imagine saying the English word sport, but “chop off” the “s” sound at the beginning. (Also listen carefully to how you say English sport then port, and notice the aspiration or “sharp breath of air” that accompanies the “p” of port but not of sport.)
Pronouncing French “b”, “d” and “g” is a little more difficult for English speakers and can take some getting used to. Recall that a French speaker deliberately tries to keep the vocal cords vibrating right the way through these sounds. Practice making these sounds and trying to “force” some extra air into your mouth while “stopping” the sound at the same time. Another technique is to imagine pronouncing them as though they were “mb”, “nd” and “ng”, and then “chopping off” the “m” or “n”.
It takes some practice, but paying attention to details such as the above can make a huge improvement to your French pronunciation and will make your speech more readily understandable to a French speaker and being aware of these differences will likely improve your understanding of spoken French.