Ik heb even gezocht en vond hier een redelijk begrijpelijke uitleg over wat SBM is en wat het doet. Tenminste ik snapte het en ben een leek op technisch gebied
What is SBM ?
In developing DAT, Sony examined, reexamined and overturned conventional approaches to A/D conversion, D/A conversion, power supply, electronic design, chassis layout and mechanical engineering. When the Compact Disc was new, its 16-bit signal delivered the full quality of the professional digital recordings of the day. But studio recorders have long since surpassed 16-bit resolution with 20 and even 24-bit performance. As professional digital systems began to exceed the 16-bit word length of the Compact Disc, Sony engineers began to ask if it was possible to capture better- than-16-bit sound quality in a standard 16-bit medium. The result of this exploration was Super Bit Mapping (SBM@) circuitry, which Sony first launched in the K-1203 professional processor. SBM circuitry then made its audiophile debut on the DTC-2000ES DAT recorder in 1994.
The comerstones of psychoacoustics are the Fletcher-Munson equal- loudness curves. Understanding how we hear and what we can hear is key to digital audio's future. A very soft perceived loudness of 10 phons requires a 1 kHz tone of 10 dB SPL. To achieve the same apparent loudness, a 15 kHz tone requires about 25 dB SPL and a 20 Hz tone requires a whopping 75 dB SPL!
The conclusion? The human ear is exquisitely sensitive to sound, including noise, in the middle frequencies, but relatively insensitive to sounds at the frequency extremes. The SBM design takes advantage of the psychoacoustic fact that the human ear is far more sensitive to low-level noise in the mid-frequencies than in the frequency extremes. So SBM circuitry uses sophisticated noise shaping to shift low-level noise out of the mid-range frequencies and into the range above 10,000 Hz, where it is relatively inaudible. The overall noise energy remains the same as standard 16-bit recording. But the audible performance is equivalent to 20-bit systems! Sony shifts the noise out of the middle frequencies, where it's most audible, and up into the higher frequencies, where it's less audible. Even though the total noise energy does not change, audible noise is substantially reduced!
To perform the Super Bit Mapping process on analog mic and line inputs, the recorder must convert the input into a digital signal of higher than 16-bit resolution. The recorder uses a pulse A/D converter and a decimation filter to convert the analog input into a 24-bit digital signal. The 8-bit difference represents more precise quantization-additional musical information and reduced noise.
Sony's Super Bit Mapping circuit uses noise shaping filters
that mirror the frequency sensitivity of the human ear.
The SBM circuit uses noise shaping filters with a frequency response similar to that of the human ear. This reduces noise in the audible range, while it feeds back and reintegrates four bits of low-level data that are normally lost in the conversion to 16-bit audio. In this way, the deck records spectacular sound from analog sources. You'll hear 16-bit recordings with musical accuracy that approaches 20 bits of resolution. Music sounds more lifelike, more vivid, more clearly audible against a background of impeccable silence.
There's more. Because the Super Bit Mapping process is "single ended," no special playback circuitry is required. You'll get the benefit of the SBM process no matter what DAT/CD player you use!
