1. Make your voice louder. Your voice is too soft.

2. Make your voice high.
3. Make your voice up.
4. ______________________
5. Speak up. They can't hear you clearly.
6. Raise your voice in reading the text.
I can't hear you clearly.
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His voice is so soft when he reads the text. In this case, which directions can we use to make him raise his voice? Do you have some more common expressions for that?

When referring to one's voice, soft means very quiet. A loud voice, of course, can be heard for a long distance. A high voice means it sounds like a child's or a woman who is singing high notes on the musical scale.

1 is fine.
2 and 3 don't mean the same as 1.
5 and 6 are fine.

His voice is too soft when he reads the text. He needs to read more emphatically.

... more loudly.
... thunderously.
... powerfully.
... emphatically.

Remember that the thesaurus is where you can find words that have similar meanings, but be careful. Not all are one-for-one substitutes!
http://www.thesaurus.com/browse/loud?s=t

To make someone raise their voice, you can use various expressions and directions. Here are a few commonly used ones:

1. Speak up: This is a straightforward way of asking someone to increase the volume of their voice. It is often used when the speaker's voice is too soft and not easily audible.

2. Project your voice: This implies that the person should use proper breath support and vocal resonance to make their voice carry and be more easily heard by others. It can be useful in situations where there is background noise or a large audience.

3. Increase your vocal volume: This gives a direct instruction to the person to raise the loudness of their voice. It is a more formal way of asking them to speak louder.

4. Raise your voice: This can be used when someone's voice is too soft or not audible enough. It suggests that they should increase the volume and intensity of their voice.

5. Be more vocal: This expression encourages the person to be more expressive and forceful in their communication. It can imply using a stronger, louder voice to convey their message effectively.

Remember, when asking someone to raise their voice, it is important to be considerate and polite in your request.