The following explanation comes from Kanchi Paramacharya (Sri Chandresekharendra Saraswathi) — translated and abbreviated from his discourse available in Tamil book ‘Deivathin Kural’ – Part 2 pages  244-249.

Our Ancestors had created very judicious ways to safeguard the Vedas and transmit them without giving chance for mistakes creeping in, even without any written source. In the formal verbal teaching,memorizing and chanting of vedas, they created so many rules so that not even a single word is miss-spelt nor wrongly intonated.

There was a time measure called ‘matra’ which is used to stipulate how long or short each syllable in the vedic mantra should be chanted. The Vedanga called Siksha had guidelines as to how to use one’s breath to cause vibration in a particular part of the human body so that the pronunciation of that word or sylable in the mantra is done to go with that vibration to get the correct sounding. The siksha gives details by comparing the swaras (notes) in music with the tonal aspects of chanting vedic mantras and identifying similarities and dissimilarities; it compares them with the sounds produced by animals and birds and give guidance through examples.

One of the greatest techniques to ensure that the words and syllables in the vedic mantras are not altered was the various chanting methods that the ancient rishis devised. They created chanting procedures that involved combining the words in the mantras in different permutations and combinations. Vakyam, padam, kramam, jatha, mala, shika, rekha, dvajam, dandam, ratham, ghanam — these were the chanting techniques followed.

In South India, we call some of the vedic pundits as “ghana baadikaL”. What does it mean? Baadam means lesson. Ghana bhadi means the level to which he has studied (i,e, upto Ghanam level) in the chanting technique of the Vedas. When you hear them chanting, you can grasp that he is chanting a segment of Veda by playing around with the same words in a phrase by combining them in different permutations. Even to listen to such a ghanam chanting is very pleasing to the ears. The natural majesty that we can feel when vedic chanting is done seems to get accentuated when we hear it as a ghanam chanting. The same phenomenon can be observed when listening to vedic chanting in other modes like jata, shika, mala, krama etc.

But the real purpose of these exercises is to to ensure that the vedic mantras are not misspelt or interchanged or jumbled up, so that the pristine nature of mantras are maintained impeccably.

The chanting of the the vedic texts in the same order in which the words are formed into sentences is known as Vakya Badam or Samhita Badam. When two sentences meet, the last word of the first and the first word of the second sentence are normally combined together. This practice exists in many Tamil verses; it is the common practice sanskrit verses too but the combination will be far more cryptic in sanskrit, there by creating scope for wrong splitting when detailing is needed. To avoid such error, there is Pada Badam technique, in which the individual words in the joints are clearly and distinctly spelt.

Thus, the Samhita Badam comes first; next is the Pada Badam. Next comes krama badam where the chanting is done by combining first and second word, second and third word, third and fourth word and so on.

The permutations and combinations will vary (in a more and more difficult way) as one progresses from Krama to jata, to chika and so on. Ghana is the most complicated of all techniques.

In the video below, an example of Krama, Jata and Ghana mode of chanting of Gayathri Mantra are explained:

Let us listen some Vedic Chanting in Kramam mode in this video below:

Let us listen to some Vedic chanting in Ghanam mode in the following video:

We know how safely life-saving medicines are preserved in laboratories by using various techniques. In a similar way, our old rishis have painstakingly created such complicated techniques in order to ensure that the Vedas which are so essential for protecting the world were kept preserved without losing their pristine purity and originality even when there was no writing involved and word-by-mouth transmission was the only method available.

When all the words and syllables of  vedic mantras tally perfectly across each of these techniques, it is a clear indication that the original texts are transmitted without any error generations after generations.

The vedic rishis also stated that considering the significance of the various chanting techniques, each upper and complicated technique of chanting has twice the value or benefit of chanting over the lower one.

Western researchers try to fix the time periods of origin of ancient texts by trying to observe the changes that could have happened in the words’ form, format or sound over long periods of histories. But such so called scientific techniques will not come to the help of determining when Vedas (which are known to be beginningless) originated because, the chanting techniques have been so meticulously crafted in order to ensure accuracy of transmission.