@Gates Azure speech service offers a demo page to test the audio content creation tool which is part of the Azure speech studio where users can create their own audio content in any language with controls over rate, pitch, volume, Intonation & Pronunciation.
If the demo is something you are looking for you need to signup with Azure and create a speech resource from Azure portal and then access the speech studio to create your audio content. The steps for the same are mentioned in this document.
The full version of audio content creation feature from speech studio which is simple and easy to use and its usage is billed against your speech resource. An azure account created for the first time comes with a free credit of 200$ for 30 days which can be used against your speech resource for the usage of this service. You can then subsequently upgrade your speech resource tier to a standard version and pay as you go as per the pricing of speech resource usage.