Raquel y ramón están en el coro. la voz de raquel es tan bonita la de ramón.

For this case we can translate the sentence into English as:

Raquel and Ramón are in the choir. Raquel's voice is so beautiful that of Ramón.

Here it is observed that the voice of two people is being compared.

The comparison is used to make a comparison between two people, things or places.

The comparative "tan (in Spanish)" + the adjective / adverb + "como" is used to indicate equality in an affirmative phrase.

Raquel y Ramón están en el coro. La voz de Raquel es tan bonita como la de Ramón.

como

Raquel y Ramón están en el coro. La voz de Raquel es tan bonita como la de Ramón.

Translation: Raquel and Ramón are in the choir. Raquel's voice is as beautiful as Ramón's.

Explanation:

Comparative conjunctions are used in Spanish to make a comparison between two or more people, animals, things or places that are mentioned in the sentence. By means of these conjunctions then some degree of inferiority or superiority can be marked between the elements or, if these are the same or not.

To form the comparisons of equality using nouns, adjectives or adverbs, use the following formula:

tan + (noun, adjective, or adverb) + como