real time voice communication by CPFSK

Hello!

I am challenging real time voice communication by CPFSK.

I am creating a flow graph like the one in the photo and testing it, but the audio is intermittently played due to audio underrun.

I am new to GNUradio and I don't know the cause and solution. What is wrong? And is my approach correct?

For the time being, I tried changing the buffer size of alsa with reference to this, but it could not be resolved. (I was able to play only when samples/symbol=1)

https://www.ruby-forum.com/t/first-time-user-fm-radio-tutorial-has-choppy-audio/233815/12

The environment is Ubuntu 18.04 and gnuradio is 3.7.13.4.

I'm sorry for my poor English.

thank you for reading!