What relationships between time sequence and nyquist bin or Dc bin?

1. What is DC bin?
2. What are FFT bins?
3. What is DFT size?

What is DC bin?

The first bin is the DC which is the sum/average of the samples in time domain. It's zero if your signal is zero mean. Otherwise it's not.

What are FFT bins?

Frequency lines are spaced at even intervals of f_SAMPLE/N_RECORD. They are commonly referred to as frequency bins or FFT bins. Bins can also be computed with reference to a data converter's sampling period: Bin = f_SAMPLE/N_RECORD = 1/(N_RECORD × Δt_SAMPLE)

What is DFT size?

If we look at the dimensions of the DFT result, we get 2+31*2 which is, again, 64 dimensions. Here is a visual representation of the matrix elements using the complex unit circle: The first row is the DC component or the bias. It only has real components.