ForstĂĄ digital lyd



ForstĂĄ digital lyd

Indlægaf DavidB » 1. apr 2013, 09:58

Dette er kopieret fra BitPerfect's facebook side. Måske andre også kan få glæde af det.

So you think you understand Digital Audio?

I'm willing to bet that most of you don't. In principle it is all very straightforward. But in practice it really doesn't quite pan out that way.

Lets start off with all the stuff that you do know.

In digital audio, the music waveform is "sampled" on a regular basis. Sampling means that the instantaneous magnitude of the waveform is measured and the resultant value stored somewhere. The "Sample Rate" tells you how often these samples are measured. The standard used in Compact Discs is 44.1kHz. This means that the music waveform is measured 44,100 times per second, and the results of each measurement are stored. The device that performs this sampling is called an ADC (Analog-to-Digital Converter).

Obviously, it is important that the precision with which the instantaneous waveform is measured is extremely accurate, and this precision is for the most part reflected by the "Bit Depth" with which the result is digitally stored. The standard used in Compact Discs is 16-bits. This means that the resultant value is stored as a 16-bit number. 16-bit numbers range from 0 to 65,535 and can take the form of whole numbers only. Here, the largest possible amplitude of the musical waveform that can be recorded corresponds to the number 65,535, and the lowest possible magnitude (which is in fact the largest possible negative amplitude, since music signals vary between positive and negative), corresponds to the number zero. By contrast, most high resolution recordings capture the musical waveform as 24-bit numbers. These numbers range from 0 to 16,777,215 and so obviously are able to capture the musical waveform in a lot greater detail.

When we play back our digital music, all we have to do is re-create the musical waveform using the stored numbers, and this is where a DAC (Digital-to-Analog Converter) comes in. Using the example of music stored in the CD format (which is commonly written in audio shorthand as 16/44.1) the job of the DAC is to grab a data value 44,100 times per second, each time creating an instantaneous voltage corresponding to the precise value encoded in the 16-bit data value. If the DAC can do this accurately, then it will recreate the original musical waveform with a precision limited only by the extent to which the original music signal can be accurately reflected by 16-bit numbers. Also - and this is obvious if you think about it - the timing of the 44,100 samples per second has to be exactly the same timing as when the music was originally sampled.

Now, here's the bit you probably don't know.

Unfortunately, one can be lulled into a false sense of security by this simplistic picture. The reality is actually quite different. You see, it turns out that it is a frighteningly complicated and prohibitively expensive task to build either ADCs or DACs that do the job I have just described. So, given that most mobile phones contain both an ADC and a DAC, how is it we manage to get around this?

The answer is a technologically and mathematically challenging concept called "Sigma-Delta Modulation" (SDM). This is basically an ultra-high-speed bit stream comprising only ones and zeros, such that at any point in time the magnitude of the encoded signal is reflected by the relative preponderance of ones over zeros. If the bit-stream comprises almost all ones, then this would represent the maximum possible signal amplitude. If almost all zeros, it would represent the minimum (or most negative) possible signal amplitude. The beauty of SDM is that - without any signal processing whatsoever - the bitstream can be fed directly into the input of an amplifier, and it takes little more than an analog low-pass filter to convert it into music. This is precisely how "Class-D" amplifiers work.

Likewise, although it is beyond the scope of this note to describe how, an ADC whose output is an SDM bit stream is a cheap thing to build, despite being an incredibly complicated thing to describe or even understand functionally.

So, in reality, with so few exceptions as to be not worth mentioning, all digital recordings are created using an SDM-based ADC, followed by a mathematically-driven signal processor which converts the SDM bitstream to a PCM data file. And likewise, all DACs take the PCM data files they receive and put them through a mathematically-driven signal processor which converts them back to SDM, which is then converted to Analog using a simple Class-D output stage.

Why should you be concerned by all this? Well, what you need to know is that, from a mathematical perspective, SDM and PCM are mutually incompatible formats. Although both are at their roots nothing more than numbers, you cannot convert losslessly from one format to the other. The conversion process invariably results in the musical data being irrecoverably "smeared" in the time domain. So, in a real-world ADC, rather than actually sampling the music at fixed intervals in time, what the ADC is actually doing is calculating what the instantaneous amplitude of the music ought to be using the SDM bit stream as its reference. Likewise for the DAC.

Many smart people will absolutely insist that PCM-based digital audio fundamentally has this, that, or another degree of perfection, based on somebody's published theoretical analysis, and if you claim to hear otherwise you are obviously fooling yourself. And based on pure-PCM assumptions, these analyses are often very convincing. Yet most serious audiophiles continue to hold that digital audio is on various levels less satisfying than good old analog.

I have developed a strong suspicion that many, many of the ills which we ascribe to digital audio may in fact be caused not by the limitations of the PCM format, but by the sonically disruptive SDM-to-PCM and PCM-to-SDM converters that live unheralded in the ADCs and DACs that inhabit the playback chain. Over time - quite a long time, I expect - I plan to experiment with this idea.
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 2. apr 2013, 02:21

Interessant læsning. Konsekvensen er med andre ord: Køb NOS DAC, også kaldet R-2R DAC. De er nemlig ikke Sigma-Delta typer, sådan som langt, langt de fleste er.
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Re: ForstĂĄ digital lyd

Indlægaf davidsh » 2. apr 2013, 11:04

Spørgsmålet er hvor stor den omtalte negative effekt ved SDM-PCM konversion egentlig er. Der skal mere viden til før jeg kan udtale mig i hvert fald.
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Re: ForstĂĄ digital lyd

Indlægaf Claus-DK » 2. apr 2013, 11:45

LarsHP skrev:Interessant læsning. Konsekvensen er med andre ord: Køb NOS DAC, også kaldet R-2R DAC. De er nemlig ikke Sigma-Delta typer, sådan som langt, langt de fleste er.


Lidt en drastisk konklusion synes jeg, du konkluderer dermed, at der de sidste 25 år kun er kommet dårligere DACchips til verden end dem der var da CDafspillere var noget nyt og spændende..

Jeg har slet ikke indblik i emnet, i det mindste ikke nok, til at kunne vurderer sandhedsværdien af det der er skrevet, men at konkluderer således ud fra et "tilfældigt" indlæg på facebook er lidt voldsomt...
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Re: ForstĂĄ digital lyd

Indlægaf DavidB » 2. apr 2013, 11:53

Nu er det jo kun en "strong suspicion". Men det er vel netop sådanne tanker, der kan udvikle nye ting? Det er der ihvertfald spændende at nysgerrigheden føre til "I plan to experiment with this idea." :-)
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Re: ForstĂĄ digital lyd

Indlægaf Claus-DK » 2. apr 2013, 12:01

Jeg er slet ikke kritisk overfor det oprindelig indlæg, det ved jeg ikke nok til, det var mere den konklusion der kom fra Lars jeg synes var lidt vild..
Er det pĂĄ facebook bakket op af kildematerial ?? eller er det ene og alene forfatteren der filosofere over emnet ?

Der er interessant læsning, men om det er kolde hårde fakta er jo et helt andet spørgsmål, det er dog altid rart med folk der "tænker ud af boksen" uden sådan nogle folk rendte vi stadig rundt med bue og pil..
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Re: ForstĂĄ digital lyd

Indlægaf DavidB » 2. apr 2013, 13:21

Blev ikke opfattet som kritisk :) yes... det er godt der er nogen der prøver at tænke ud af boksen.
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Re: ForstĂĄ digital lyd

Indlægaf FrederikS » 2. apr 2013, 17:52

Der er ingen forskel andet end hvordan DAC chipsne er implementeret. Der er meget mere ydelse at hente ved et godt konstrueret kredsløb end ved at bruge en dyere DAC chip. Man skal ikke kikke så meget på chippen mere på hvordan det er skruet sammen. Det er slf noget bøvl i og med det er sjældent at fabrikanter giver meningsfulde specifikationer på deres produkter.
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 2. apr 2013, 19:58

OK. Meningen med min post var vel bare, at ved at fravælge Sigma-Delta DAC chipsene, så slipper man en fejlkilde. Dvs. med R-2R typerne undgås denne digitale konvertering fra PCM til bitstream, som ifølge indlægget er inkompatible digitale koder / signaler. That's all.

Den oprindelige post bruger udtrykket om denne digitale konvertering: "sonically disruptive", hvilket sĂĄ stĂĄr for egen regning, men dog et informeret synspunkt, mĂĄ jeg antage.

At der er meget, meget andet, der også skal gøres rigtigt, for at lyden bliver optimal, er så en anden sag.
Senest rettet af LarsHP 2. apr 2013, 20:05, rettet i alt 1 gang.
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Re: ForstĂĄ digital lyd

Indlægaf Anda » 2. apr 2013, 20:01

Hvilke R-2R er de mest interessante?
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Re: ForstĂĄ digital lyd

Indlægaf davidsh » 2. apr 2013, 20:24

Men man undgår dog ikke SDM til PCM konversionen helt ved at købe en NOS DAC, da den vel er brugt under selve optagelsen af musik osv.?
Hovedtelefoner: B&O H6, Hifiman HE-500, Hifiman HE-5LE, Koss KSC75, Sennheiser HD800, Sennheiser Momentum, Stax Sigma (NB), Stax SR-307, Stax Lambda Signature
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Re: ForstĂĄ digital lyd

Indlægaf FrederikS » 2. apr 2013, 20:36

Sådan som jeg lige kan læse mig frem til så skulle produkterne af den konvertering ikke være tilnærmelsesvis tæt på noget der kan blive hørbart. Tror det er hip som hap hvilken teknologi der bliver brugt. SDM er billigt og stabilt og R-2R er dyere og det virker ikke som om at der er noget at hente der, hvis der var ville firmaer som BB/TI, AKM osv. nok have udviklet en high end model på den teknologi. TI kan jo bare genoptage produktionen af 1704 serien, men istedet ser man at diverse system integratore der laver virkelige high end ting vælger SDM både musik produktionsudstyr og hifi. Især med musik produktion er dette meget sigende da de ikke er blege for at hælde rigtige penge efter deres gear.

Bare mine tanker omkring det!
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 2. apr 2013, 20:56

Anda skrev:Hvilke R-2R er de mest interessante?

Burr Brown's / Texas Instruments PCM1704UK er meget kendt og anerkendt. Det er en 24bit chip, der kan køre hi res.
Mange sĂĄkaldte NOS DAC'er bruger 16bit Philips chip'er.
Ellers har Metrum Acoustiscs lavet DAC'er med industri-DAC chip'er, der også kan køre hi res. Disse chips skal (også) være rasende dyre.
Se Octave trĂĄden og NOS DAC trĂĄden.
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 2. apr 2013, 21:03

FrederikS skrev:Sådan som jeg lige kan læse mig frem til så skulle produkterne af den konvertering ikke være tilnærmelsesvis tæt på noget der kan blive hørbart. Tror det er hip som hap hvilken teknologi der bliver brugt. SDM er billigt og stabilt og R-2R er dyere og det virker ikke som om at der er noget at hente der, hvis der var ville firmaer som BB/TI, AKM osv. nok have udviklet en high end model på den teknologi. TI kan jo bare genoptage produktionen af 1704 serien, men istedet ser man at diverse system integratore der laver virkelige high end ting vælger SDM både musik produktionsudstyr og hifi. Især med musik produktion er dette meget sigende da de ikke er blege for at hælde rigtige penge efter deres gear.

Bare mine tanker omkring det!

Jeg har set flere high end producenter anvende netop PCM1704UK i deres topmodel - slet og ret fordi de efter at have testet top-DAC chip'er er kommet frem til, at den er den bedste pĂĄ markedet - selv efter at Sabres 9018 chip er kommet pĂĄ markedet ...

Jeg siger ikke, at PCM1704 DAC'er dermed er de bedste, men at denne chip tilsyneladende stadig er anset som den bedste af nogle producenter, når det kommer til "no compromise / cost no object" produkter. Audio-gd er ikke de eneste hvad angår dette, men jeg husker ikke lige nu hvilket andre mærker/modeller, der har været tale om.
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 2. apr 2013, 21:05

davidsh skrev:Men man undgår dog ikke SDM til PCM konversionen helt ved at købe en NOS DAC, da den vel er brugt under selve optagelsen af musik osv.?

Det er selvfølgelig rigtigt. Det eneste audiofile nørder kan gøre er, at optimere sig eget udstyr - herunder have færrest mulige kompromiser. Jitter er et andet veldig godt sted at se.
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Re: ForstĂĄ digital lyd

Indlægaf Claus-DK » 3. apr 2013, 00:44

Lars@ Ahh så er jeg med og jeg kan sagtens følge dig i den tankegang, Murphys law gælder jo overalt, så færre fejlkilder giver færre fejl i sidste ende..

Jeg opfatter de fleste NOS chips som værende mere bløde i lyden, det nogen måske ville kalde "rørklang" om man så foretrækker det eller de moderne som er lidt mere "rene" og skarpe i lyden er nok mere et spørgsmål om både personlig og musik smag end noget egentligt teknisk..

Det skal dog siges at den SA 1.32 (fra GD) der er på tour kan et eller andet ganske særligt i mine ører, jeg holder på den anden side også meget af den jeg har med en Sabre chip i, måske har jeg slet ingen smag ... .. LOL
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Re: ForstĂĄ digital lyd

Indlægaf Claus-DK » 3. apr 2013, 01:05

Jeg tillod mig at sakse igen igen og har forelagt tingene for mine "guruer"..

her er hvad de har svaret indtil videre..
http://diyah.boards.net/index.cgi?board=digitalmusic&action=display&thread=29

OgsĂĄ lige en reklame for et nyt forum, skabt af tre af mine online-venner gennem flere ĂĄr..
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 3. apr 2013, 17:35

@ Claus-DK
Vi er selvfølgelig enige om, at det i sidste ende handler om, hvad man hører, og om man kan lide det. NOS lyder blødere, skriver du, og det kan der måske være noget om, men NOS DAC og R-2R DAC er ikke det samme. Læg mærke til, at det vigtige er ikke er non-oversampling, men multibit DAC overfor Sigma-Delta princippet. En multibit aka R-2R DAC kan sagtens køres med f.eks. 8X oversampling - så som PCM1704 chip'en. Faktisk er standard indstillingen på min Reference 7.1 netop 8X oversampling. Det er imidlertid fortsat en R-2R DAC chip, der gør arbejdet - blot med oversampling. Her får man fordelene ved både oversampling og R-2R.

Da jeg var inde på Tera Player hjemmesiden faldt jeg (igen) over denne side, der handler om R-2R chip versus Sigma-Delta. Det er selvfølgelig også en (informeret) persons mening - og ikke indiskutable fakta.:
http://www.mother-of-tone.com/conversion.htm

Sakset fra ovennævnte side:

Conversion Techniques

R2R
In the CD-format chapter you have seen that digital numbers are translated into a staircase signal, and by rounding the steps, we get something that pretty much resembles the originally captured signal. This translation process from numbers into voltage steps, is what happens in a R2R DA converter which is sometimes also called a "ladder-DAC" or "multibit-DAC", as resistors (the R's in R2R) are configured as an ascending series of voltage dividers. Such a R2R converter is a static device, in that it is able to generate a clean voltage (with 16 bits resolution there are 65536 different voltages) and hold that voltage until another number is converted, or if numbers repeat - for an infinitely long time, while maintaining an extremely low noise level. In order to achieve a certain level of performance, the resistors (R's) inside the converter chip must be precisely trimmed, which can make a device very expensive to manufacture, especially when true 24-bit resolution is required. Some companies were famous for their R2R converter chip designs, such as Analog-Devices, Burr-Brown and Philips.

The 'El-Cheapo' Method
In order to avoid the required precision in the manufacture of R2R converters (and save manufacturing costs), another conversion technique became very popular. In this conversion technique, a single switch replaced the precision resistors of the R2R DAC, and it was believed (and shown to a certain extent) that if only the switch was toggled fast enough, one could also achieve many different voltages. If for example the switch is more often switched to 5V than to 0V, and if that switch-signal is run through a low-pass filter then the output voltage will also be closer to 5V, than to 0V, plus lots of noise. This fast switching technique is employed in sigma-delta conversion and it is also the technical foundation of the newly introduced SACD or DSD format.

As a 16 bit R2R DAC is able to generate 65536 different static voltages, and a single switch can only generate 2 different voltages (hi and low), a high switching frequency (usually in the range of a couple of MegaHertz, and achieved through oversampling) is necessary for proper operation and thus, much noise will be produced by the switching process in a sigma-delta converter. In fact, for any practical application, the noise-level is much higher than the signal that is to be reproduced. Therefore, this inacceptable high noise-level is shaped into higher-frequencies, as it is believed that high-frequency noise is outside the human listening range and will not degrade sound quality.

As a side effect of this high-order noise-shaping even higer noise levels are generated, residing in the high-frequency region. To our surprise, in the technical specification of those sigma-delta DACs very low noise-levels are mentioned, and by reading the data-sheets, one could have the illusion, that a decent sound quality would be attainable by such a device. In fact, the total noise-output is never stated in the data-sheets, and measurements only mention in-band-noise up to 20kHz, suggesting that higher frequency noise has no effect on fidelity. Of course with this eye-closing practice only those can be fooled that also have closed ears.

In plain english: sigma-delta DACs are coarse noise-generators and when measured the way they should be measured they never make it to 16-bit resolution, don't even think about 24 bits. As some engineers realized that the el-cheapo method did not lead to satisfying fidelity, because with 1-bit switching performance the quantization noise level was just too much, new converters came up, being called "multi-level sigma-delta". By increasing the number of voltages from 2 (1-bit) to 5 or more (multi-level), the quantization noise could be reduced. As this was still not satisfactory, some companies started introducing more levels and coined the term "multibit sigma-delta), as they now use 32 or 64 voltage- or switching-levels, which make up 5 or 6-bits.

Now imagine how much money was spent in research & development to make DA-converter chips cheaper, and in the end just finding out, that more and more levels - more resolution - has to be introduced in order to make them listenable. Just have a short break to think about it. The more levels you introduce to sigma-delta - the more bit resolution you realize, the better it gets. Where does that lead to? Exactly. It leads just all the way back to R2R converters, which have high-resolution, high accuracy and very low noise.

R-2R vs Sigma-Delta chips, sinus-trappe.JPG
R-2R vs Sigma-Delta chips, sinus-trappe.JPG (61.07 KiB) Vist 13200 gange


The key issue that I want to address here is noise. A R2R DAC can convert noise-free, whereas any sigma-delta DAC relies on the noise in order to randomly shape the immense quantization error. Even if the noise is technically specified to be outside the human listening range, and also specified to be easily filtered away, any real-world implementation of any sigma-delta DAC will tell your ears a different story. And Soundwise? In science, the experiment decides if a theory is held valid or discarded. This is of course difficult when a sound quality is subjectively assessed, as science only deals with instruments, as the experiment for being considered valid, must be repeated consistently. This is the core of all arguments of the following type:
A: It is flawless and perfect in any scientific, engineering and mathematical way.
B: But it sounds so bad.
or the other way:
A: You cannot do that at all. It is totally wrong and you can measure numerous kinds of distortion.
B: Hey, now its just right. This is the way a saxophone sounds :-)

Subjective Evaluation

R2R/Multibit/Ladder DAC:
What I personally like with R2R converters, is their ability to reproduce a wide variety of timbres. A cymbal can really sound like a cymbal, not like crinkling a piece of paper. A piano can have body. It is the richness and diversity of complex harmonic structures that a well done multibit or R2R DAC is able to produce, which can make it a very musical and real sounding device. Position of instruments is rock-stable. Sound has balls, and at the same time precision. It can drive. If there is any sonic signature at all, it is one which could best be described as "chocolate-like".

Sigma-Delta DAC:
What I personally dislike with any sigma-delta DAC I have listened to up to now, is the lack of reproducing a voice's or instrument's timbre, and the lack of all other positive aspects of R2R DACs, as mentioned above. Instead of being able to enjoy the richness and variety of different sounds, I have the impression that everything sounds the same, or has the same imprinted character, which could best be described as nervous fizzle. There is no tone and no body. No balls, no precision, no transparency and no drive. What is left is the annoying sonic signature, ranging from "acid to pink hiss". The more levels or bit-resolution are introduced in a sigma-delta converter, the less annoying the sound becomes. The worst sound can be achieved with 1-bit modulators, as found in DSD, respectively SACD. Apart from SACD being a complete waste of storage space, the achieved resolution is low, and the musical presentation ranges from "very lame without detail and drive" to "more detail but very acid".

PS: For being fair, some people relate what I call "nervous fizzle" to "very wide and open soundstage". I consider this an issue of listening level, or perhaps - in better words: personal preference. To me, the realness of a musical presentation is to a large part determined by correct timbre (tone) of instruments and voices.

PPS: Recently I was able to audition a very expensive and high-performance CD-player that runs on 4x AD1955 sigma-delta converters per channel. Although that was definitely the best and smoothest sigma-delta presentation I had heard by then, I was not completely satisfied. One or two octaves were underrepresented in the lower end, soundstage was quite narrow, although none of the typical switching noise was apparent. But subjectively the worst and most consistent problem was the inability to play different timbres. Every instrument sounded the same, as if covered with a gloss of plastic, not PVC but a higher quality plastic...
Squeezebox Touch (Fidelity Audio digi. mod.) > Audio-gd Ref 7.1 DAC > Audio-gd Master-6 > HiFiMan HE-6
HiFiMan HM-901s > Atrox V2 > HE-6
Bærbart: HiFiMan HM-901s (Bal. amp) > Unique Melody Miracle
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Re: ForstĂĄ digital lyd

Indlægaf FrederikS » 3. apr 2013, 20:05

Den steppede waveform til sidst er forkert ingen DAC kan lave den med mindre man giver den en sinus + squarewave på en eller anden måde. Det ligner bare et forsøg på at vise en sinus kurve alle tre, da den sidste er helt forkert så er de andre det nok også.

Den støj der kommer i en sigma delta ligger i frekvenserne der er langt over det hørbare med noise shaping og et filter.

http://en.wikipedia.org/wiki/Delta-sigma_modulation
http://en.wikipedia.org/wiki/Resistor_ladder
FrederikS

 
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Re: ForstĂĄ digital lyd

Indlægaf LarsHP » 3. apr 2013, 21:06

Claus-DK skrev:Lars@ Ahh så er jeg med og jeg kan sagtens følge dig i den tankegang, Murphys law gælder jo overalt, så færre fejlkilder giver færre fejl i sidste ende..

Jeg opfatter de fleste NOS chips som værende mere bløde i lyden, det nogen måske ville kalde "rørklang" om man så foretrækker det eller de moderne som er lidt mere "rene" og skarpe i lyden er nok mere et spørgsmål om både personlig og musik smag end noget egentligt teknisk..

Det skal dog siges at den SA 1.32 (fra GD) der er på tour kan et eller andet ganske særligt i mine ører, jeg holder på den anden side også meget af den jeg har med en Sabre chip i, måske har jeg slet ingen smag ... .. LOL

Nu har jeg ikke hørt en DAC med Sabre chip i, men efter hvad jeg har læst, så er Sabre's force detaljering blandt andet, så din oplevelse passer godt ind i det. SA-serien fra Audio-gd er (som du selvfølgelig ved) Kingwa's musikalske serie, så denne blødhed kan faktisk være pga. hans forstærkerdesign ("diamond difference design"). Min Ref 7.1 lyder i hvertfald ikke blødt i sammenligning med Metrum Octave, som Ketil B har lånt mig i disse dage. Der er det Octave'n, der i den sammenligning lyder blødt (og begge har R-2R DAC chip). Octave har et regulært non oversampling (NOS) design, mens min altså kører med 8X oversampling.

Det folk i negativ forstand kalder "digital lyd", tror jeg handler om jitter først og fremmest. Denne skarphed i de øvre frekvenser, som jitter kan give, er nok ofte synderen der. Sigma-Delta "historien" kommer nok i anden række, men ifølge nogle fagfolk (her tænker jeg på både producenter og hi-fi anmeldere) spiller dette også ind. R-2R DAC'erne siges at have mere ground'et lyd, med mere tonal farve, mens Sigma-Delta typerne ofte beskrives som slankere og med mere fokus på de øvre frekvenser og f.eks. lysende klarhed som positivt karaktertræk. De anmeldere, der taler for R-2R DAC'erne, mener at disse er mere naturligt lydende og mindre "digitalt" lydende. Dette er selvfølgelig fine nuancer, ikke store, markante forskelle. Implementering og analogdel har naturligvis også stor betydning, men det er andre og meget mere komplicerede sager ... som jeg ikke kan sige ret meget om.
Squeezebox Touch (Fidelity Audio digi. mod.) > Audio-gd Ref 7.1 DAC > Audio-gd Master-6 > HiFiMan HE-6
HiFiMan HM-901s > Atrox V2 > HE-6
Bærbart: HiFiMan HM-901s (Bal. amp) > Unique Melody Miracle
LarsHP

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