I am currently feeding my lossless iTunes library through the optical channel into a Marantz DAC94 [a classic over-engineered old-school DAC utilising the almost mythical TDA1541s], which is then passed on into an active Linn System [Ikemi / Kairn / 2xLK140 / Ninka].
I have had the opportunity of hearing several of the newer UK DACs with their multifarious upsampling techniques. I have not appreciated the new sound.
I am going to draw an analogy and i would be interested in what people have to say.
1. Is upsampling the audio equivalent of video upscaling?
2. Is Upscaling just visual trickey? An illusion that consistently fails to convince us?
1080p televsions are all the rage right now, but [in the UK at least] DVDs are not actually created/formatted to output at 1080p, but rather at either 720p or lower.
Watching a movie at its original [ie formatted resolution] means you see the original image. Keep your plasma at 720p or 576i [depending on the format of the DVD] and you get a clearly defined picture. When you upscale the image you may get "more" on the screen but it's not real is it? it's the upscaler playing digital tricks. it's a computer programme and/or an algorythm trying to "fill in the gaps" of a series of moving images.
And these predictions are often wrong. this, to me, is most apparent on close ups of human faces. upscaling just fails to accurately predict the range of movement of a human face. the movement is just too infinite and random. it's as if, at any moment, the blur and "add ins' of upscaling make the face look like its about to morph into something else. we see pinpoint accuracy in the parts of the face that aren't moving and strange blurs in the bits that are [most noticeably the lines of the forehead.] i often feel like i am watching an early 90s science fiction movie: human faces are forever on the edge of mutating into terminators...
personally i would rather watch and listen to what's actually there: not some digital predictive illusion of continuity. if there's a rock slide i want to see the rocks sliding, not a computer approximation that decides its actually a waterfall.
and i think that modern upscaling DACs may do something similar.
just a thought...
Posts: 76
Intereting thought, itll be, er, interesting to see what
people have to say.
Dell 5150 (XP Home) with M-Audio Delta Audiophile 2496 Sound Card*Beresford TC-7510*NAD C320BEE*Monitor Audio BR2s*Vivanco Silverflex speaker cable*No-name interconnect from amp to PC*Mission Stance stands
Posts: 3144
Hi iansen - That's certainly
Hi iansen - That's certainly an interesting analogy and I've thought the same thing in the past. Since I'm not an engineer I won't attempt to talk technically about this topic. I will say that upsampling is done for many reasons, including reducing jitter. There are a couple conversations around here where this topic has been discussed and there really is no consensus on upsampling. Good, bad or ugly it really depends on the implementation by each manufacturer. Some manufacturers MAY be looking for a higher number on their spec sheets while others MAY be attempting to improve sound quality.
Chris Connaker
Founder
Computer Audiophile
Posts: 117
Upsampling audio is really
Upsampling audio is really different than upsampling video. Audio is simpler, only voltage, where video has color, intensity etc..
Audio upsampling algorithms run the gamut. Some are better than others. In general I have found that hardware upsamplers are inferior due to limited functionality. The best are upsamplers that re-write the file and take as much time as they need to do the computation, such as Adobe Audition and R8Brain. These can take overnight to do an album. Next best are upsamplers that do it on the fly as you play the track, such as SRC and SSRC in Foobar2000. They have less time and require low-latency and lots of compute power, so this limits their effectiveness. They are superior to hardware upsamplers though. SRC is mostly what I use.
Upsamplers attempt to "fill-in" the missing musical information. They take a "best-guess" at what it would have been based on the previous and next information. If they are really good at this, the difference between the actual 24/96 recording and an upsampled from 16/44.1 to 24/96 is actually very small. This means that dynamics, smoothness and other positive attributes of the original hi-res track will be in the upsampled track. Listening tests on good upsamplers verify that this is indeed the case.
Steve N.
Empirical Audio
http://www.empiricalaudio.com
Posts: 55
Yes & No
Oh my, that is my favourite area: improving sound with software :)).
As Steve said it before me, it is different compared to video. But one thing is the same for both: the quality differs between several upsamplers or upconverters. I don´t know how video upconverters function so I´ll concentrate on Audio.
Mostly upsamplers are used to get around the limitations of a cheap or bad DAC. With limitations I mean that these DACs have a bad performance when anti-aliasing is performed. In order not to have aliasing effects in the listanable audio area (20 - 20.000 Hz) everything above must be eliminated. So every DAC uses a very steep frequency cut-off at 20.000 Hz. Sometimes these algorithms are not that good so in the end they are hurting the sound. With upsampling you shift this 20.000 Hz of anti-aliasing further away to 40.000 Hz where you can´t hear it anymore. What you can´t do of course is recreating a signal that came from an original 24/96 source that was downconverted to 16/44.1. An upsampler or resampler uses an interpolation filter in combination with an anti-aliasing filter and fills up the spaces between the original 44.1 kHz with zeros when upconverting to 96 kHz.
So, an upsampler really is an oversampling filter without the D/A converter, because that is also what oversampling does. That means you could have frequencies over 20.000 Hz, but they are erased because of the believe that they can destroy loudspeakers or create problems for the amplifier. With 95 % of upsamplers you have a frequency response that goes from 20 to 20.000 Hz - beyond that is nothing. With good upsamplers the quality of the outcoming signal is the same as the original 16/44.1 data.
However, some people in the industry always knew that there could be more. WADIA & Pioneer for example. The spline algorithm is nothing else as an oversampling filter where the following anti-aliasing filter is not steep anymore and very soft. There the aliasing components are deliberate. Aliasing mirrors the frequencies starting with 22.050 Hz up to the double amount of 44.100 Hz. The data mirrored is the data from 20-22.050 Hz. Pioneer called this "Legato Link". Wadia and Pioneer did this to improve impulse response. The major drawback of steep aliasing filters is audio impulse that has pre- and post-ringing, means it adds ripples to the audio signal just by filtering above 20.000 Hz. With things like Legato Link this could be avoided - in the end you´ll get a frequency response up 44.100 Hz (faked of course) and nearly perfect impulses.
There is only one resampler on the market that can be configured to achieve this thing written above: iZotope RX Resampler. With this you can shift the cutoff frequency up or down, influence the kind of ripple (more or less pre-ringing) and configuring the steepness of aliasing cutoff. It is fast and produces perfect results, it really is very good. You can also use it for re-creating your standard resampler like SSRC or else. Then it sounds like a very good version of these "normal" resamplers.
With original 24/96 data, downsampled with iZotope and then upsampled again with iZotope I was able to find a perfect configuration that actually "recreates" 60-70 % of the sound of original 24/96 material without the errors of bad up- or resampling (smearing, less precision). So I´ll say Upsampling CAN have a benefit - if you use the right tools. Have a look here for pictures and more description (I hope I´m allowed to do that): http://www.thesoundtrackzone.com/viewtopic.php?f=35&t=323
E-MU 0202 USB wired with Monster USB Cable --> Audioquest King Cobra --> (sometimes) Corda Arietta --> Sennheiser HD-600