Upsampling e Oversampling na conversão D/A do Redbook (em Inglês)

"Theory of Upsampled Digital Audio" - Doug Rife

http://www.mlssa.com/pdf/Upsampling-theory-rev-2.pdf

-

"Upsampling or Oversampling?" - John Atkinson

http://www.stereophile.com/asweseeit/344/

It is important to remember three things about all of these products:
1) other than making active the lowest 8 bits of a 24-bit word, no new audio information is created by any of these products
2) as susceptibility to word-clock jitter increases with sampling frequency, it is always possible that upsampling audio data can make things worse, not better
3) no matter how good these upsampling products can sound—and the dCS, Bel Canto, and MSB products indeed sound excellent—there is no conceptual difference between them and traditional CD playback systems.
I am now convinced that the sonic differences we have heard and reported on are due to the different choices in digital filters made by the designers of these products with respect to the number of taps, passband ripple, and stopband rejection, and to changes in the jitter performance.

-

"Oversampling Versus Upsampling: Differences Explained" - Alison Aulph

http://www.soundstagehifi.com/gettingtechnical/gettingtechnical200311.htm

"High-​End Audio: Science or Snake-​Oil?" - Beat Stamm

In 2006 I was invited to a local high-end audio store’s annual show where I had a chance to listen to an unusual demo.
A salesman for expensive turntables, along with an editor of Stereophile fame, tried to convince the audience of the inferiority of CDs compared to vinyl records.
Equipment were top of the line Wilson Audio speakers ($135k/pair), VTL tubed monoblock power amplifiers and associated pre- amplifier ($60k, if memory serves), and speaker wires that could make your average garden hose jealous (I’ll come back to those esoteric speaker wires below).
In the first part of the demo, the turntable salesman played a record he had bought the night before, in a second hand record store in the University district.
Before lowering the needle into the grooves he expressed his joy and pride about his find ($5, no k here).
It sounded like a used record: Dusty.
Would it hurt to clean the record before playing it on a stereo that cost more than my three bedroom house in 1999?
I tried to listen to Charlie “Bird” Parker, ignoring the pops and clicks of the vinyl, and there was a saxophone in a club. Not a particularly enjoyable listening experience, but it sounded like a saxophone nonetheless.
In the second part of the demo the salesman played a CD he had made from the above record, also the night before.
Something like connecting the line-out of the phono stage to the line-in of the laptop, have the laptop quantize the vinyl, clicks and pops and all, such as not to make the comparison too obvious, and then play it back through similar means.
As far as I remember, it was level matched, and the track sounded just like the record.
It was, after all, a faithful, digital copy of the record.
Once the saxophone began to play, the difference became painfully obvious.
The crude analog-digital-analog conversion process easily managed to ruin my listening experience even more.
Behind all the pops and clicks the saxophone sounded synthetic.
Somehow the audience was left with the worst of both worlds.

continua - http://www.beatstamm.com/scienceorsnakeoil.htm

Upsampling

An Upsampler is a digital-to-digital converter (DDC) capable of converting digital audio data at one sample rate to a higher sample rate.
The term "Upsampler" was first used by dCS in 1998 during development of the dCS Purcell.
Some other manufacturers appear to have confused the term "upsampling" with "oversampling", which is a similar process used in good audio DACs for many years.
They have missed the point that upsampling is an intermediate step intended to provide enhanced data to drive an oversampling DAC.

Some positive observations that help to characterise the effects of upsampling in a dCS system:

1. Upsampling to progressively higher sample rates makes progressive improvements to fine detail, sound stage depth and image separation. So, the sound quality increases as you upsample CD data first to 24/88.2, then 24/176.4, then 24/352.8 kS/s.

2. Converting 16/44.1 to 24/44.1 kS/s makes a worthwhile improvement to the fine detail, so the resolution is important also.

3. If data with a higher information capacity is presented to the Ring DAC, sonic improvements are reported.

One present view is that upsampling works by breaking the DAC's oversampling function down into 2 steps, presenting the DAC with finer, smoother data, making the DAC's job much easier and more accurate.

fonte dCS