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In Reply to: RE: The Four Truths of Digital posted by lorraine116 on November 7, 2008 at 02:35:45
"Truth One: DSD is a 4-8 bit recording system, not 1. This means it gets decimated and oversampled - two things the scheme was trying to avoid in the first place."The bitstreams comprise of an intermediate conversion method, in the case of DSD, a central conversion for all consumer formats. Whether oversampling is involved is irrelevant- It's probably utilized for Redbook CD, but it doesn't have anything to do with the conversions themselves. (I might be wrong on this.)
I really doubt that any modern conversion uses decimation (aka "downsampling"), unless the intent was expressly to convert the signal to a lower-resolution format. Decimation loses resolution, which cannot be recovered.
"Truth Two: 16-bit 'audiophile' CDs contain 20-bit level resolution and have since 1993."
This is false. The data wordlength on "audiophile" CDs is no different from that of other CDs..... The data wordlength on *all* CDs is 16-bits. (The CD wouldn't even play otherwise.) CDs can be encoded with "dither" to maximize potential resolution (provided the signal prior to digitization is of higher resolution to begin with and the playback uses filtering), but the end product is always a 16-bit 44.1 kHz sampled CD. (Dither is not an application unique to "audiophile" CDs, and I'm sure CDs with dither existed prior to 1993.)
"Truth Three: The limit of human hearing is 20-bit level resloution."
Although I agree it's roughly 18 to 20 bits, just stating something without explanation doesn't automatically make it "truth." (Studies with exhaustive listening trials would be required to determine this.) The residual noise in most electronics is also a limiting factor.
"Truth Four: Digital is hundreds of times lower in distortion vs. analog but its distortions are spread-out spectrally and are hard to pin down. They're removing these, at last, in the latest playback gear."
Digital is indeed "hundreds of times lower" in distortion vs. analog, but because harmonic components of frequencies greater than 22 kHz, including harmonics from distortion, are **removed** in the digitization process, for Redbook CD. The harmonics are filtered out in the A/D process (to prevent out-of-band frequencies from reflecting into the audio band and stored on media), and filtered again in playback (to prevent audio signals from reflecting out of band- not as critical as A/D filtering). The vintage of the player or playback technology has nothing to do with this.
Or in other words, if the pre-digitized signal has 5 percent harmonic distortion above 11 kHz, it will effectively be reduced to trace levels, because the brickwall filtering *literally* removes all harmonic components which make up the distortion. The effect is similar for higher (but not all) harmonics for signals below 11 kHz. I don't think this is necessarily good because the signal is altered, albeit "measuring better."
Higher resolution digital media would measure higher in top-octave (10-20 kHz) THD because the incoming distortion products are actually "preserved" if sampled at a much higher rate. The harmonic components are stored on media instead of filtered out. And MP3 would measure lower THD in its top octave (lower frequency range) than CD over MP3's frequency range.
In my humble opinion, the THD distortion figure for CD and lower-resolution digital playback is the most-useless specification in audio.
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