If anyone knows the reason,please help me.
I can see the meter moves properly,and the waves can be seen.So the sound is recorded.I can hear the audio after recording.BUT I can never monitor the sound when recording.I almost give up.
have you clicked the loudspeaker icon on the track you wish to monitor whilst recording? You’ll need to un-click it once you’ve finished or you’ll not hear the playback.
Alternatively, is there not a monitor mix on your audio interface? I don’t know the Tascam FW1884 but my Tascam (and most other interfaces) have a knob that allows to to mix input and out-put so you can monitor the input before it gets to the DAW.
In many situations the program Preference “tapemachine style” is a good choice.
You will no longer have to care for the Brown Monitor button.
See the Manual for how it works.