The key vowel sound of each word is one of the most important sounds that helps listeners understand you. In addition, vowels are quite complicated. Therefore, helping you learn to produce the key vowel sounds is one of the fastest and most effective ways to improve. Blue Canoe also helps with consonants, but typically only after prioritizing feedback on stress and vowel sounds.
Why are vowels complicated? The first reason is that each vowel letter can produce several different sounds, and each vowel sound can be represented by several different spelling patterns, which highlights the separation between spoken and written English. Also, most differences in dialects are due to a slight difference in movement or placement of the vocal tract while producing vowel sounds. There is great dialectical variety of how native speakers produce vowels, but not so with consonants. We like to say that the consonants are stars, whereas vowels are the space between the stars. That ‘space between the stars’ is where the meaning is, which is central to comprehensibility.
Generally speaking, consonants are easier to produce and are more straightforward in regards to what sounds they make. For example, when you see the letter ‘m’ you know with a high level of certainty that it represents the sound /m/. Some consonants do make a few other sounds, as in the letter ‘c’ which can represent the /k/ or /s/ sound, but most are “what you see if what you get.” Also, consonants are easier to describe how to articulate; you can describe where your tongue, lips, and/or teeth should be touching (unlike vowel sounds, which are produced with no contact of the tongue, lips and teeth). Finally, one of the main functions of consonants is to show tense or number, as in the difference between ‘work’ and ‘worked’ or ‘play’ and ‘plays.’ The consonant sound tells us these details, but is not central to the main meaning.