The Harmonica is a very subjective instrument. The quality of the notes, and in fact any note coming out at all, depend almost entirely on the player. The small reeds inside the harmonica actually chop the air that passes through the chamber and reed slot, and it is this action on the column of air that produces the sound. The properties of that column of air make a huge difference in how the reed plays and how it sounds. This air column is produced and refined inside your body, through processes that are mostly unconscious to most people. There are at least two main categories the air column affects:
1. The tone, depth, and quality of the sound. This is why professional players sound like they are playing a huge, powerful, beautiful musical instrument, while sometimes beginners can get no sound whatsoever to come out of a hole.
2. The pitch of the note. Again, pros learn to manipulate the pitch (by changing that column of air), and this bending produces subtle expressive introductions or exits from notes, and also entirely new notes that are not built into the instrument. Again, no sound at all will come out of the instrument if a player is applying bending techniques outside of the narrow range where they work (this often happens unconsciously with beginners).
One example is that in every class of beginners, a definite percentage of some will think the 2 draw on their C harp does not work. They will either get no sound, or a foghorn like honk When checked, their harp will be perfect, but the sound is happening like that because they are unconsciously bending the note (even though they dont know how to bend)their natural resonance, and the tension they have in their lips, throat, etc. is creating a situation where their air column is now forcing the draw 2 to NOT play. The remedy is to bring awareness to all these qualities as they bring the harp up, to play very gently with an open mouth so all the lower draw holes are gently sounding, and to gently bring their lips in from the sides, so they gradually hear just the 2 draw. Sometimes players will get this right away, and sometimes it takes weeks of retraining before they can play the 2 draw with an open, unrestricted, air column.
Any restrictions in your air column become even more pronounced on a Chromatic harp, because now your lips are further removed from the reeds, and the space created by the mouthpiece/slide/etc. serves to amplify quirks in the air. Many players who switch to chromatic from being used to diatonic cannot get reeds to sound properly at first. They need to practice the gentle, open, delicate breath to discover how the reeds respond, and then they can gradually play normally.
Of course the harmonica must be built and set up properly, so the reeds work. If you are having problems with a reed or hole we (Seydel USA) will gladly check your harp out and fix or adjust if necessary, but the first recommendation is to notice what happens when you go to play, and to patiently tune into everything in your body that is producing the air and directing it to the harmonica.