192/24bit DAC's vs. 96/24 DAC's

Discussion in 'Archived Threads 2001-2004' started by jorge c, Jun 18, 2002.

  1. jorge c

    jorge c Auditioning

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    Hello,

    Can anyone explain to me what DAC means and what its function is in the different channels. Does the higher mhz make that much of a difference in the sound.

    Thanx
     
  2. Charles Averty

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    Hi,

    DAC means Digital Analog Converter.

    Why is a higher frequency better?

    In a digital to analog conversion two things are important: the clock precision ans the filtering.

    1/ Assuming your source is a DVD at 192kHz:
    1.1/If your DAC is 192kHZ, only a certain amount of filtering to eliminate frequencies above 96kHz is required, because the two frequencies are the same.
    It is called anti-aliasing filtering. It is required before any conversion from digital to analog, due to some maths I don't think you're interested in.
    (there is another filter called recontruction filter but it is failry simple)

    1.2/If your DAC is 96kHz, you need a lot of additional processing on top of the 1.1: you need a good steep filter to eliminate all frequencies above 48kHz. Because you're more likely to have more energy below 96 than above, the filter must be more efficient.

    2/ If your source is lower than 192 and digital, using a good sampling rate converter to upsample to 192 makes sense, for several reasons:
    You can remove a good amount of jitter (depending on the quality of your own 192kHz clock of course).
    Once you have upsampled your signal, your filters become cheaper/easier to design for the reasons mentionned above.
    The problem is that processing at 192kHz is a lot more expensive than processing at 96kHz in terms of DSP frequency.

    Hope this helps and that I have not made too many mistakes,

    Charles
     
  3. Kevin C Brown

    Kevin C Brown Producer

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    Is that true? "Upsampling" helps improve jitter? I didn't know that. [​IMG]
     
  4. Mark Tranchant

    Mark Tranchant Stunt Coordinator

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    Let's try to help the original question with a simpler answer.
    Digital audio sources such as CD store their information as a long string of numbers, which represent the original sound waveform. There are two key specifications to a digital audio stream: the resolution (number of bits) and sample rate (number of kHz).
    Resolution
    The ADC (analogue to digital converter) that converts the analogue signal to a digital signal looks at the input every so often, and assigns a number to the voltage at that time. This is called sampling. If it worked as percentages, think of the ADC as assigning a percentage from 0% (no signal) to 100% (full signal).
    However, the waveform is "AC" - it alternates positive and negative about a zero centreline. So think of 0% as "full negative" and 100% as "full positive" signal, with 50% as the zero point. This only gives 100 "steps" to the digital signal, which turns out to be not nearly enough for a decent reproduction of an audio signal. Also, electronics prefers binary numbers (made up of bits - 0s and 1s), which favour numbers of steps that are a power of two (an n-bit number allows for 2^n steps).
    The familiar 16-bit CD signal stores each number in 16 bits (e.g. 0101011110101001), which gives 65536 "steps" in the signal. Newer 24-bit formats use 8 more bits, giving 16777216 steps for a finer reproduction of the signal. Many tests have shown that 16 bits is ample for all but the most discerning listener.
    Each channel in the signal (2 for stereo, 6 for 5.1) gets its own number for every sample.
    Sample rate
    The sample rate is simply the rate at which the ADC samples the signal. A CD signal is digitized into two 16-bit numbers (one for each of the two stereo channels) at a rate of 44100 samples per second - or 44.1kHz.
    The maximum frequency that can be digitized is simply half the sample rate: 22.05kHz for CD. This is known as the Nyquist theorem after the guy who worked it out. Attempting to sample higher frequencies will result in the DAC "hearing" a lower frequency in the signal, which is called aliasing distortion.
    You can demonstrate this to yourself: draw a waveform on graph paper with pencil - include some wiggles within the large squares. Put a mark with pen at the intersection of the big square boundaries with the waveform. Rub out the pencil and try to draw the waveform back using just the pen marks. You can't deduce anything about the features that are smaller than a large square.
    To avoid this distortion, the input signal must be filtered to eliminate high frequencies. For CD, this requires a steep filter to include 20kHz audible sounds but knock out everything above 22kHz. It's hard to design a good filter to do this. A better solution is to use a higher sampling rate like 96kHz.
    DACs
    So far, I've talked about ADCs and how the digital signal is stored. The DAC must read the samples at the same rate as they were stored, and attempt to reconstruct the original waveform from them. Typically, these just hold the sample level between samples to give a stepped output, which is thenn low-pass filtered to smooth the steps. Theoretically, more complicated curve-fitting techniques could be used.
    Hope that helps!
     
  5. jorge c

    jorge c Auditioning

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    Thank You Everyone for your replies, they have been very helpful, but is it really worth spending the extra money for the 192/24. Can the average person notice much difference in the sound.
     
  6. Charles Averty

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    With the new formats 192kHz DACs is going to become standard before end of the year....

    Yes resampling improves jitter.

    It is not the actual resampling of course, it is the better clock and a small input buffer (the buffer absorbs the jitter). But the better clock cannot work without a complete resampling filter.

    Of course the recording jitter can never be absorbed, but all the jitter produced in digital format can be corrected (CD groove, CD player clock, cable)
     
  7. Peter Johnson

    Peter Johnson Stunt Coordinator

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    I would worry less about the specs, and more about how it sounds.

    Oversampling happens in all DAC's, not just 192kHz DACs. 192kHz DACS are capable of decoding a signal sampled at 192kHz. The problem is...there is no software that actually does this.

    In other words..its a marketing gimmick.

    Implementation of the DAC is far more important than its specs.
     
  8. Charles Averty

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    Does 192kHz justify the price difference? I believe not.

    Is 192kHz sampling justified? I believe not. I believe 96kHz to be largely enough.

    At 192 the design costs are increased so much that I don't think one can really get a improvement of quality.
     
  9. Louis_JBL

    Louis_JBL Auditioning

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    Check out the harman kardon avr-125. i just picked it up from www.jandr.com for $299. its has a 192/24 and don't let the 45 watts X 5 power rating scare you off. this thing will blow all the receivers out of the water in this price range. my friend has the avr-110 and i've never seen his volume over -10db.
     
  10. Ed St. Clair

    Ed St. Clair Producer

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    Numbers.
    Engineering.
    To very different aspects to 'our' hobby.
    On paper: 192.
    In listening test: depends, on parts and/or engineering [as well as personal preference].
    When 24 bit DAC's first came out, many [if not all], were inferior to the best 20 bit DAC's. Better on paper, but price/production/preformance were not up to snuff.
    Look for 192 DAC to improve greatly in price and performance by mid-03, if not sooner.
    Isn't it great to be in the computer age?
     
  11. John Kotches

    John Kotches Cinematographer

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    Peter,

    192K isn't a marketing gimmick in a DVD-Audio player, there are titles on the market that are sampled at 24bit/192K.

    24/192K DACs for at least two channels are a requirement in any DVD-audio player.

    Regards,
     
  12. Bill Adlhoch

    Bill Adlhoch Stunt Coordinator

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    john, that 192 KHZ doesnt do you much good when 90% of all decent HT gear has to down convert it to 96Khz
     
  13. Kevin C Brown

    Kevin C Brown Producer

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    Bill- The 24/192 info on a DVD-A disc played on a DVD-A player is not digitally transferred to a receiver or pre/pro. It's analog. But you still need those DACs *within* the player to get the 24/192 info off the disc, converted to an analog signal.
    Me personally? I wouldn't buy a piece of gear right now with 24/96's when 24/192's are already available.
    But y'all have to decide for yourselves... [​IMG]
     
  14. John Kotches

    John Kotches Cinematographer

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    Kevin,

    Correct, with the exception of some very pricey all-digital solutions (Denon 5803+9000 about $8K, upcoming Meridian 568+598 between $12 and 14K (pricing not finalized) and the Meridian 861+800 34K and up).

    Regards,
     
  15. Kevin C Brown

    Kevin C Brown Producer

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    John- I am suitably corrected! [​IMG]
     
  16. Harvey S

    Harvey S Extra

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    I think maybe the original question that started this thread still hasn't been answered ! What reason is there to prefer a receiver (not a dvd player) with 192khz DACs over the same receiver with 96khz DACs (e.g. Marantz 7200 vs 6200). Assuming that the listener can only hear frequencies up to 20 khz or so, why pay more for the ability to reproduce frequencies in the range 48khz to 96 khz that probably aren't present, can't be amplified by the receiver or transduced by the loudspeakers anyways, and couldn't be heard if they were ?

    Did I misunderstand something?
     
  17. John Royster

    John Royster Screenwriter

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    A receiver with 192 Khz DACs will sample analog sources at 192 Hz, meaning higer resolution and hopefully putting any filter noise much higher than our 20Kz limit. While the music is digitized at that high rate the receiver is processing the sound for things like bass management, speaker distance and most importantly effect.

    Think of it this way. More bits means more precision. Kindof like math. .007 is more precise than the rounded .01

    Now as to hearing that extra resolution is subject for a heated debate.
     
  18. Harvey S

    Harvey S Extra

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  19. Ferran Mazzanti

    Ferran Mazzanti Stunt Coordinator

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    Hey Harvey S,
    just checking at the american Marantz server, 6200 and 7200 specs, I've seen both models have 192/24 DAC conversion for front left and right only. At this point, seems that both models are exactly the same...
    And John, it's true that maths say 192 is more resolution than 96, but what really matters is, as you say, if the difference can be really heard. Any other thing is no more than technical stuf... [​IMG]
     
  20. John Royster

    John Royster Screenwriter

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    I hope I made my post clear. Maybe I didn't.:b I slipped up calling a DAC a ADC. Anyway they work in conjunction, the processing occurs on the digital information that is sampled with the Analog-to-digital convert. You now have twice the information to work on, 192K/sec vs 96K/sec.
    The big fallacy is the "you only need to sample at twice the frequency" rule. SACD and DVD-A use higher sampling rates to capture a more accurate representation of the waveform. Many insturments have overtones well above our hearing range - that's why different saxaphones sound the way the do and so on. So there isn't a pertfect sinewave for all instruments rather a very complex set of harmonics and overtones on said sine wave. Also another reason why good power amps have a frequncy response well above 20K, sometimes 100 Khz, is to reproduce those overtones and high frequency ripples/overtones.
    So point is higher sampling frequencies can capture that information. This is all nice and techy but hearing a difference is where I like to put my money and prefer as much analog as I can find. CDs sound edgy and "digital". SACDs don't (for the most part).
    Thanks for listening to me ramble.[​IMG]
     

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