Hi, I have just come across your question. I appreciate this may no longer be timely but I am adding a couple pointers in case they can help others.
For isolating or segmenting speech in low-noise recordings, the function detectSpeech should work just fine. This will return start and stop times of all signal regions where speech is detected, but no text "transcription" of the actual speech content. Based on that info you thn can label each section of your recording as voiced or unvoiced.
Only for advanced projects requiring the application of machine learning and signal processing to solve the same problem in noisy conditions, I would recommend starting from this example: Voice Activity Detection in Noise Using Deep Learning
