The ghunnah is defined as: a nasal sound that is emitted from the nose. This is a required characteristic of the  and .  The ghunnah  cannot be separated from these two letters and is an inherent part of their makeup. 

The ghunnah is not a letter but a characteristic of these two letters, but it has its own distinct place of articulation. 

The ghunnah  is articulated from : the hole in the nose that continues back  towards inside the mouth.

It is a nasal sound coming from the nasopharynx without any influence from the tongue.  If you hold your nose closed you will not be able to produce the ghunnah sound, but the letters themselves that have this associated sound with them are not articulated from the nose.

The  and  with a shaddah

Anytime the letters  and  have a shaddah on them, they are held for a length of time, and the ghunnah described above is present during the lengthening.
 A shaddah represents two of any letter.  When the symbol for a shaddah (a small ) is over any letter, there are two of that same letter recited, the first with a sukoon, the second with the vowel written above or under the shaddah mark. 

The length of time to hold the  and  that have a shaddah on them cannot be given in counts, instead the timing must be picked up from a teacher who has a strong background and has learned their recitation at the hands of masters in recitation.  The concept of two counts for a ghunnah is not a correct concept.  The ghunnah has different timings depending on whether there is a shaddah, or if there is hiding of the  or , or if the two letters are recited clearly with a sukoon on them, or a vowel.  The longest timing for the ghunnah is when there is a shaddah on one of the two letters. 

If we take a look at a few aayaat, we can pick out where the  and  have a shaddah on them, and therefore the sound of the ghunnah should be lengthened when reciting them.

The next two aayaat there are three different  that have a shaddah on them. They are in red.  Each of them are held for a length of time, equal to each other with a ghunnah (nasalization) accompanying the lengthening.

In this aayah, there are two different with a shaddah on them. One in the second word, the other in the third word.  Each of them should be held for a period of time, equal to the other, elongating the sound with a ghunnah emitted from the nose. 
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