• Download audacity from its offical page.
• Install audacity into your system.
• Open audacity, set Recording Device to Stereo Mix ([Audio Device name])
• This will only record audio from playback, not from microphone.
• Remember not to play any other audio/music except the one you would like to record.
• Come back to the eSilence > Text To Speech
• Put your text to speak inside Text to speak box
• Once ready, return to audacity and click the Record RED button
• Come back to the eSilence > Text To Speech, and tap Speak button.
• Tap Stop button if you need to stop the speech.
• Remember not to play any other audio/music except the one you would like to record.

With audacity, you can do whatever you like with the recorded speech. For more information about using audacity, please visit Audacity Manual.