"That's what I miss out of all this synthesized music - it starts to lose dynamics"

Glenn Frey's quote speaks with the absence of dynamics in synthesized music. By dynamics, he is describing the variety of volume and strength in a piece of music. Synthesized music is often developed utilizing a computer system, and as a result, it can do not have the subtle nuances and changes in volume that are present in music developed by a live band. This can make the music sound flat and uninteresting. Frey is revealing his preference for music created by a live band, as it has more characteristics and is more engaging to listen to. He is suggesting that manufactured music can be too uniform and predictable, which it can do not have the feeling and energy of music developed by a live band.