User Manual

Multichannel Monitoring Tutorial Booklet (M2TB) rev. 3.5.2

Masataka Nakahara : SONA Corporation

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[Fig. 9] 6.1 Discrete

2-2. Encoding and compression methods

2-2-1. Encoding methods

When encoding an analog signal into a digital signal, the encoding performance is largely dependent on

two parameters; the sampling frequency (fs[Hz]) which corresponds to the sampling precision of the time

axis (frequency axis), and the number of bits used for quantization (Qb[bit]) which corresponds to the

sampling precision of the amplitude (loudness). For both fs[Hz] and Qb[bit], higher values allow the

occurrence of digital encoding noise to be minimized. This means that for both fs[Hz] and Qb[bit], higher

values are generally interpreted as “higher audio quality.”

In two-channel media, a CD is encoded at fs=44.1 kHz/Qb=16 bit, and DAT is encoded at fs=48

kHz/Qb=16 bit. The dynamic range for these types of media is approximately 96 dB. In multimedia,

DVD-Audio is encoded with six channels of fs=96 kHz/Qb=24 bit, giving a dynamic range of

approximately 144 dB. This type of encoding is known as multi-bit encoding; the upper limit of the

frequencies that can be reproduced is determined by fs/2, and Qb essentially determines the dynamic

range.

In contrast, the single-bit high-speed sampling method uses the minimum number of quantization bits —

Qb= 1bit — and instead samples at an extremely high sampling frequency. In the Super Audio CD (SA-

CD) developed by Sony and Phillips, this is called the DSD (Direct Stream Digital) method.

Because single-bit high-speed sampling expresses the amplitude of the sound not as a stepwise amplitude

of Qb but rather by the density of the sound pressure. It is said that this encoding method is closer to the

physical characteristics of the sound wave itself. However since Qb=1 bit, the quantization noise when

encoding is much greater than with multi-bit methods and an extremely high sampling frequency is

required in order to remedy this. The Super Audio CD uses a very high sampling frequency of 2.8224

MHz with Delta-Sigma conversion, shifting (noise shaping) quantization noise outside the audible range,

and delivering better than approximately 120 dB of dynamic range in the audible range. The recording

bandwidth is said to be DC through 100 kHz.

In this way, there are currently two ways to digitally encode an audio signal; “multi-bit methods” and

“single-bit high-speed sampling methods.” Generally, “PCM” or “LPCM” indicate “multi-bit methods.”

In contrast, since the Super Audio CD is currently the only mass-market media that uses single-bit high-

speed sampling, single-bit high-speed sampling and DSD are often used as synonyms.

Production

Playback by end-users

Surround processing

DVD-Video

LFE

Media

Master