[Discuss-gnuradio] for sending sound from modulation digital is need syncing Tx and Rx???

[Stack Programer]

i want to use modulation digital like fsk,psk, ask for sending sound,

i have a hackrf and rtl-sdr.

for sending sound from modulation analog like fm or am everything is ok,for sending 

digital modulation from projects on githubs:

https://github.com/argilo/sdr-examples

i had not good receive sound,i had a question:

for sending digital modulation is necessary  syncing rtl-sdr and hackrf???

please help

best regards stackprogramer