If you want more information on the photos in this video, which have parts of the mouth drawn in, see this video on the parts of the mouth.

How to make this sound:

The audio is now available for download thanks to user Slava from Cherkessk, Russia: Download mp3

Video Text:

The 'uh' as in 'supply' vowel sound, also known as the schwa.  This is the most commonly occurring sound in English, uh, uh.  It only happens in unaccented syllables, like the first syllable of supply or about.  To make this sound, the mouth remains very neutral and relaxed, uh, but the lips have the part.  And the teeth, uh, will be close but not quite touching, uh, uh.  The tongue remains flat and forward, very relaxed, uh, lightly touching behind the bottom front teeth.  Uh, supply.

Here we see the 'uh' as in 'supply' vowel on the right, compared with the mouth at rest. Notice that the jaw drop is minimal. Here, parts of the mouth are drawn in. The soft palate, as in all vowels, is raised. Note also that the tongue is slightly pressed down in the back. This means that the tongue, though very relaxed, is slightly lower than when it is at rest. You can see at rest, that the tongue comes up to where the top teeth are, whereas in the 'uh' as in 'supply', it is slightly lower. Sample words: sofa, about, occur. Sample sentence: Today and tomorrow we'll walk around the city. Now you will see this sentence up close and in slow motion, both straight on and from an angle, you so can really study how the mouth moves when making this sound. 

Today, the first syllable is the schwa, the teeth make the T, and you can see the jaw dropped just a hair. -Day, and, the jaw drops again for the aa. Tomorrow. Again, tiny jaw drop on the schwa sound. -Morrow. Lips form the W. We'll, and again, W for walk. Around, the first syllable is a schwa, around. The, quick schwa. City, teeth come together to make the ss sound and the tongue up to make the D sound which is how we pronounce that T. City. Again from an angle. Today, teeth come together to form the T and then separate very slightly, there it is, for the schwa.

Today, tongue forms the 'aa' as in 'bat', and the jaw drops a bit more to make that sound for 'and'. Tomorrow. Again the teeth part just a bit to make that schwa sound. -Morrow. We'll walk, the lips form these two W's. We'll walk, and now when it comes in from this sound, it's going to hit the schwa. Around. Tongue through the teeth for the, another schwa, the jaw dropped just a bit. City. The tongue touched up to make that D sound in city.  That's it, and thanks so much for using Rachel's English. 

International Phonetic Alphabet symbol: []

This sound, called the 'schwa,' is the most common vowel sound in the English language, according to Wikipedia. For more information, see this page, also on Wikipedia.