The voice that you hear when you sing--your voice--may sound different to you than it does to others hearing you. What to you may sound like a full resonance may actually be a very nasal sound. Here's a way to check.
Some vowels tend to get that nasal quality. For example, you may think you're pronouncing the vowel in "moon" the same as the vowel in "you" (consider the tenor part in the tag to "I'll Be Seeing You"), but "moon" starts with a nasal consonant "m" and ends with a nasal consonant "n" so if you're not careful, the "oo" sound can also become nasal. Try it yourself with the technique in this video.
When you do this, you may feel that buzz on sounds other than "m" and "n". The "r" sound also has this tendency. So what do you do? The video says to lower your tongue in the back, but it's not clear how to do that.
The problem is that the back of your throat is too closed, so you have to do something to open it more. Not necessarily all of the time, but particularly during these sounds. One thing you can do is to keep the tip of your tongue touching your lower teeth whenever you're singing vowels. By doing this, you move your tongue forward and make more room in the back of your throat.
Another thing you can do is to open your jaw wider whenever you're holding a vowel sound. This doesn't mean you should try to open your lips any wider. That will happen somewhat when you open your jaw, but you don't want to exaggerate it. It also doesn't mean you should constantly try to open your jaw wider. That will create an unnatural sound. The movement should be smooth, not quick, so only think about opening wider when you have the time, when you're singing a sustained vowel.
If someone tells you that you need to open your mouth more, they probably mean to open your mouth more for sustained vowels. Vowels near "m," "n," and 'r" sometimes get closed off, so be particularly aware of it in those contexts.
A very useful vocal exercise
The title of this video is misleading. It actually describes a technique that gets your tongue in the proper position while singing.
Although the video says to change from "sing" to just "ng," I find it more natural and easier to relax when I use the words "sing" and "song." So for example: "sing" "oo" "song" "oo" repeated. Using both "sing" and "song" puts the tongue tip in slightly different positions, which prevents me from keeping it artificially fixed.
It's important that you stress the "g" part of "ng" otherwise the nasal sound of "ng" carries over to the next sound, so think, "sing-gah" to make sure that the sound is clean.
Some consonants aren't articulated this way easily, particularly "l" and "r," but if I sing "singer-songer" I get a softer "r" rather than a pirate "arrrr." "T"s, "d"s, and "l"s ("single-songle") can also be articulated this way with a little concentration, and you end up with smoother vowels following them than with the tongue tip near the roof of the mouth.
I also found that when trying to reach high notes on words with "r" and "oo" in them that I would get my tongue back in my throat and end up pressing to get to the note. If I think about keeping my tongue in the "ng" position, I don't do that.
This open throat position is not only important when singing out, but also when breathing in, and you have a lot less to think about while you're breathing in. For practice, I try to take a full breath as quickly as possible, then sustain a note, another breath, another note, etc. All the while I'm trying to get my throat as open as possible while breathing in and then keeping it that way while singing out. I try to keep the breath as quiet as possible because this means less turbulence, less drying of your throat, and smoother, more efficient breathing.
When you're singing, you can think about this exercise whenever you sing a "ng," "g," or "k" sound. "Do my crying-gand my sighing-glaugh at yesterday."
Try it yourself. Figure out some variations.
The answer is on the tip of your tongue
(note: if this video stops in the middle, click on the gear in the bottom right of the video that says "Change quality" set it to 240p and replay the video)
Although you want your tongue to rest relaxed against your teeth when singing, it's helpful to press the top of the tip of your tongue against the lower teeth or the space below while learning the technique, because it probably doesn't want to stay there.
It may be difficult to pronounce some consonants when you first try this. The "ng" vocal exercise from Eric Arceneaux above can help.
Now, you may think that there is a particular way to pronounce a consonant, but consider the shape a ventriloquist places his lips when he makes an "ee" sound, an "oo" sound, or any other sound. The ventriloquist tries to keep his lips in the same place, but has no trouble pronouncing sounds that are very different. If we were to look at the waveforms, we might see some differences between the "oo" sound he makes when speaking naturally and when speaking for his dummy, but we hear both sounds as "oo."
In the same way, by changing the way we articulate sounds, we can make them sound smoother, cleaner, and sweeter as we sing. If you find that your singing voice is too "dark," or "nasal," or "heavy," this technique will help.
Head voice? Chest voice? Hwa?
If you've ever been given the advice to "Just breathe," or "More air," and you thought you were already breathing, this may help.
There are a lot of misconceptions about head voice, chest voice, falsetto, and mixed voice. This might sort it out. It also describes some techniques that will help you to sing without tension and to use voice quality to better interpret a song.
Taming the wild larynx
No, it's not a wild cat. Your larynx, also called your voice box, is where your voice comes from. Here's an explanation of how it affects the sound of your voice.
Here's another video with some good techniques for controlling the position of your larynx.
You can pick your favorite cartoon character to describe the low larynx sound. I first heard about it from Roger Love's book [on the main "Learning" page] where he described it as Yogi Bear, and I'm a Yogi Bear fan from way back.
This Yogi Bear sound can help you to expand your range to higher notes and to lower notes. Start singing as Yogi Bear, then sing a scale upward or downward. You should be able to go beyond your usual range. Of course, it's no use sounding like Yogi when you sing, but once you get there, try experimenting, relaxing a little, until you get the sound you want.
Then when you have to sing those high or low notes and you start to feel tension in your voice, or you start to sound like you're screeching, think of Yogi, and try to get that same lower larynx feeling and that smooth sound.
It also works across any "break" in your range. With enough practice, the break will disappear.
It's very important, though, that you don't forget proper tongue placement when you do these exercises. You must keep the top tip of your tongue in contact with your lower teeth. This can be difficult at first because the larynx and the tongue tip are going in opposite directions, but keep at it. These two techniques together are key to a quality sound.