2009年12月10日 星期四

Audio 知識

Sound --> ADC --> Digital Form ( CD, SACD, XRCD )
Digital Form --> DAC --> Analog --> Amplifier --> Speaker

Digital Form Enhance
1. Upsampling ( Dithering + Noise Shaping(Shaving?) + ...

24bit/176.4KHz Best
24bit Dynamic Range ( Equal Segment) is 144dB
20bit Dynamic Range is 120dB
16bit Dynamic Range is 96dB
XRCD Dynamic Range is around 108dB

Formula

20 * log10( 2^24 ) = 20 * 7.22 = 144 dB

SNR = Dynamic Range + 1.76dB

The dynamic range of human hearing is roughly 140 dB.

2. Digital Transfer
by SPDIF

by XLR

by HDMI

transmiiter IC --> wire --> receiver IC--> I2S ( DAC accepted form ) --> DAC




DAC

Dynamic Range
SNR
THD ( Total Harmonic Distortion )
IMD

PCM1792 Datasheet recommended using NE5534 & LT1028 op

The operational amplifier recommended for the IV circuit is the NE5534, and the operational amplifier recommended for the differential circuit is the Linear Technology LT1028, because its input noise is low.


The circuit of Figure 37 can realize the highest performance. In this case the output level is set to 4.5 V rms and 129 dB S/N is achieved (stereo mode). In monaural mode, if the output of the L-channel and R-channel is used as a balanced output, 132 dB S/N is achieved (see Figure 39).
Balanced Output (XLR, TRS)

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