x264 quantization question

[yaous]

Quantization (no matter whether it's deadzone or trellis) takes some DCT coefficients and a qscale (qscale = 2^(QP/6)), and divides the coefficients by the qscale. Deadzone and trellis differ in how they round the result of the division.
Ratecontrol chooses QP for a whole frame. If AQ is enabled, then AQ modifies the QP for some macroblocks.

what does Quantization Matrice do in quantization?

is it a just threshold when takes DCT coefficients?

[Dark Shikari]

The quantization matrix coefficients raise or lower the precision of quantization for each coefficient.