Sorry for the confusion and thanks for reaching out to us.
What is free product? - There are 40+ services that are always free, which called free products like Azure Speech Service as you mentioned.
Those are all the free services - https://azure.microsoft.com/en-us/free/free-account-faq/#free-services
What is a free trial? - When you sign up for an Azure free account, you get $200 credit. In the first 30 days, any services you use beyond their free amounts will be deducted from that $200 credit. When you've used up your $200 credit or 30 days have passed (whichever happens first), you'll need to upgrade by moving to pay-as-you-go pricing.
When you create your Azure free account, you start getting monthly free amounts of certain types of services. If you move to pay-as-you-go pricing within 30 days or after you’ve used your credit, you’ll continue to receive monthly free amounts of popular services until 12 months after you created your account. After that, if you’re using any of these services, they’ll continue to run and you’ll be billed for them at pay-as-you-go rates.
What is a free monthly amount? - There is a free monthly amount you can not exceed as a free tier, please check on https://azure.microsoft.com/en-us/free/free-account-faq/#free-services for the limitation as below.
I hope my answer helps!
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