Ordinary English is not delivered at a rate you are unable to process. It is delivered with sounds removed, words joined and consonants swapped, so what defeats you is not that the stream is too fast but that it no longer contains the sounds you are listening for.
That distinction decides what to do next. If the problem is speed, the answer is more exposure and more patience. If the problem is that the sounds are absent, exposure alone will not supply them, and what you need is to learn what gets removed and when, which is a short and surprisingly regular list.
Eight processes that change the words
- a sentence you can read is a sentence you cannot hear, and every process below is a reason why.
- an apple runs together. A final consonant attaches to a following vowel, moving the boundary the ear is listening for.
- next day loses the t. A consonant between two others is dropped, which is why facts and fax sound identical.
- ten pounds becomes tem pounds. The n moves to match the p that follows it, automatically and unconsciously.
- did you becomes didja, and would you becomes wudja. A d or t before a y sound fuses into a new consonant.
- going to becomes gonna, and got to becomes gotta, in every register including formal speech.
- I would have becomes I would've, which sounds identical to would of and is why native speakers write that error.
- law and order gains an r between the two vowels in British speech, a sound that is in neither word.
Four things happen, and they happen at the same time
Take did you get it, which is four short words and is almost never said as four short words. The d at the end of did collides with the y of you and the two fuse into a single sound closer to a j. The vowel in you collapses to almost nothing. The t at the end of get is not released, so there is no audible t at all. And the whole thing runs together with no gap between the words for a listener to cut at.
Every one of those is regular. The same collision produces the same fusion every time it happens, in would you and could you and had your, so this is a rule you can learn rather than an accident you have to survive. What makes it hard is only that four of them run at once, and knowing three still leaves you with a sentence you did not catch.
Where it stops: the wrong diagnosis
Almost every learner reaches the conclusion that native speakers talk too fast, and that conclusion sends them somewhere useless. They look for slower material, and slower material is material in which the deletions have been put back: a recording made for learners, or a person kindly enunciating. Both are versions of English that nobody speaks.
So the practice succeeds and transfers to nothing. Comprehension of the slow material climbs steadily, real speech stays exactly as opaque as it was, and after a year the learner concludes that their listening is simply weak. Nothing in the experience points at the actual cause, because the actual cause is a property of the material they abandoned.
Slow the recording, never the speaker
The playback speed control on any video player is the tool, and it is free, universal and usually one click away. Set a clip to three quarters speed and every deletion, fusion and reduction stays exactly where it was while you get more time to hear it. That is the opposite of what a person does.
It replaced asking somebody to repeat it more slowly, which is the reflex and which returns a different sentence: a speaker slowing down re-inserts the sounds they had dropped, so you are handed a version that does not contain the thing you failed to hear. The limitation of the control is that below about half speed the audio starts to smear and the fusions become hard to place, so the useful range is narrower than the slider suggests.
What it looks like when it goes wrong
The recognisable failure is a word boundary in the wrong place, and English is full of pairs that make this unavoidable: an ice cream and a nice cream contain exactly the same sounds in the same order, and only context separates them. If you are reconstructing sentences word by word, you will land on the wrong one regularly.
The quieter failure is a missing auxiliary. In I could have gone the have reduces almost to nothing, so a learner hears I could gone, decides they misheard, and does not register that the perfect was there at all. Whole grammatical structures go unheard this way for years.
What the machinery words reduce to is on the twenty that English hears and most languages do not, and which words get compressed in the first place is settled by why English stresses some words in a sentence and swallows the rest. Both sit under being understood the first time you say it.
All of that is about hearing it. The other half is that these processes are not optional for you either: speech in which every word is fully separated is slower to follow, so learning what gets deleted is a speaking instruction as much as a listening one, and where it pays is real speed, real accents, no subtitles.