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Thread: Audible Jitter/amirm vs Ethan Winer

  1. #91
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    Quote Originally Posted by Phelonious Ponk View Post
    Not my question but...are these other digital artifacts reduced by lowering jitter?

    P
    Don is more of an expert on the internals of DACs but in my view, no. Non-linearities in the DAC are there for a number of other reasons. Jitter simply adds other forms of distortion to it.

  2. #92
    Member Sponsor [Technical Expert] DonH50's Avatar
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    Sorry, I dozed off... What specific artifacts? Some forms of distortion are actually reduced by adding noise (that's what dither is, after all), while others are not (or little) changed. In all cases, if you add jitter, SNR is degraded (lowered, reduced, made worse, whatever). Digital artifacts to me are something added between ADC and DAC, in the digital domain, and the impact jitter has depends on the type of error (artifact).

    I will say as a general rule Amir is right -- jitter adds another error source to what's already there, and gets RSS'd along with everything else.
    Don Herman
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  3. #93
    Quote Originally Posted by Phelonious Ponk View Post
    Given a good enough recording, I've been able to identify the brand and model of an acoustic guitar, I should be able to pick up on an obvious distortion.
    I have this same hangup with pianos. It seems obvious to me, because the tone of a Steinway "D" varies greatly from the tone of a Yamaha C3, or a Bosendorfer 290. I may be biased, since I play the piano.
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  4. #94
    Member Sponsor [Technical Expert] DonH50's Avatar
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    Pianos and guitar are a bear to record and to reproduce well. However, I suggest that, given time and training, you could learn to identify many forms of distortion you are now hearing but ignoring or neglecting. There is a catch, naturally; sometimes, ignorance really is bliss! It took me years to learn to identify subtle error sources in recordings and various sound systems, and more years to train myself that the music, not the noise, is what matters and to listen through the artifacts.

    BTW, in my experience musicians are among the least-discerning listeners, not because they hear poorly, but because they listen for different things. (I am a musician so hopefully I can get away with that statement.) Critiquing a recording, a musician is more likely to say (e.g.) "Did you hear that chord? The brass didn't flat the third!" than "Did you hear the jitter noise in that chord?"

    While I am rambling, I will reiterate my position that many audiophiles would faint if they actually spent time in a studio and saw the amount of processing that goes on behind the scenes in most recordings...

    Anyway, my 0.000001 cents - Don
    Don Herman
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  5. #95
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    I always like to look at Wikipedia articles to see if they can save me some typing and they do indeed in this case! http://en.wikipedia.org/wiki/Digital...alog_converter

    DAC figures of merit:

    Static performance:
    • Differential nonlinearity (DNL) shows how much two adjacent code analog values deviate from the ideal 1LSB step [1]
    • Integral nonlinearity (INL) shows how much the DAC transfer characteristic deviates from an ideal one. That is, the ideal characteristic is usually a straight line; INL shows how much the actual voltage at a given code value differs from that line, in LSBs (1LSB steps).
    • Gain
    • Offset
    • Noise is ultimately limited by the thermal noise generated by passive components such as resistors. For audio applications and in room temperatures, such noise is usually a little less than 1 μV (microvolt) of white noise. This limits performance to less than 20~21 bits even in 24-bit DACs.


    Frequency domain performance:

    • Spurious-free dynamic range (SFDR) indicates in dB the ratio between the powers of the converted main signal and the greatest undesired spur
    • Signal to noise and distortion ratio (SNDR) indicates in dB the ratio between the powers of the converted main signal and the sum of the noise and the generated harmonic spurs
    • i-th harmonic distortion (HDi) indicates the power of the i-th harmonic of the converted main signal
    • Total harmonic distortion (THD) is the sum of the powers of all HDi

    If the maximum DNL error is less than 1 LSB, then D/A converter is guaranteed to be monotonic. However, many monotonic converters may have a maximum DNL greater than 1 LSB.

    Time domain performance:
    • Glitch energy
    • Response uncertainty
    • Time nonlinearity (TNL)

  6. #96
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    Quote Originally Posted by amirm View Post
    Let's review an observation you had before. Please confirm if you are still standing by these statements before I comment further:
    Actually, I withdraw my comment from yesterday because of something you explained previously that I forgot. Earlier you said that jitter affects low-order bits rather than being a fixed number of dB below the music. So if that's true, then jitter is not some level below the music but at a fixed level. Maybe you or other experts here can clarify.

    Quote Originally Posted by amirm View Post
    please tell me if your views above in not hearing jitter in soft passages at any level would also apply to all artifacts in digital conversion combined.
    I hesitate to speak about "all artifacts" here because it's so broad. This thread is about jitter only.

    --Ethan

  7. #97
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    Quote Originally Posted by Ethan Winer View Post
    Actually, I withdraw my comment from yesterday because of something you explained previously that I forgot. Earlier you said that jitter affects low-order bits rather than being a fixed number of dB below the music. So if that's true, then jitter is not some level below the music but at a fixed level. Maybe you or other experts here can clarify.
    Here is a simplified way to look at it. Jitter creates unwanted harmonics. Once those harmonics rise up to the same level as what a single bit of audio sample would represent, then you would lose that bit of accuracy.

    Let's say you have a 16 bit system with 96 db of signal to noise ratio. The last bit of that sample is responsible for that last 6 db of performance (-90 to -96 db). Now if jitter causes a sideband which has 6 db of magnitude, then it obliterates the signal that last bit would represents, making your effective performance now 15 bits. If jitter creates 12 db of distortion products, then you lose 2 bits. So jitter eats your resolution bit by bit from the right hand side (least significant bits first).

    If during A-to-D conversion, higher fidelity system was used to create it than you are using to play it due to jitter, then the distortion is not below music. But rather, it is taking what used to be represented by music data and replacing it with distortion products.

    Note that I am not saying you can't hear the music below the distortion products. You can. But that the DAC performance is compromised to the level explained above.

    I hesitate to speak about "all artifacts" here because it's so broad. This thread is about jitter only.

    --Ethan
    But how we look at it is no different. Either one has the position that all the bits in a DAC matter or not. You can't on one hand say that 14 bits is good enough for some music but not for other and in the next breadth say that if jitter robs you of the same 2 bits, it doesn't matter. Or the fact that you heard the difference between 16 and 24 bits but somehow, can't hear the difference between jitter-less 16-bit audio and one that has been degraded to 14 or 15 bits due to jitter. Quantization noise is harmonic distortion and if you can hear that, then you should have no problem hearing jitter effects. And quantization noise when going from 16 to 24 bits is much lower than the effect of jitter on 16-bit samples.

  8. #98
    Member Sponsor [Technical Expert] DonH50's Avatar
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    There are some mistakes and points not well explained in the Wikipedia article, but the parts quoted by Amir are good enough imo. I keep thinking I should contribute, in my spare time (ha!)

    Regarding DNL, DNL > 0 implies a "long" code, so DNL of +2 at some transition is OK -- the output will still be monotonic (i.e. codes going 0, 1, 2, 3, 4 as desired even though 2 may last a long time...) DNL < 0 implies a short code, and if less than -1 you can end up with codes going e.g. 0, 1, 3, 4 -- there ain't no two! That is nonmonotonic. Some applications are more sensitive to nonmonotonic codes than others. And, you may see an N-bit DAC (or ADC) specified as M-bit monotonic, particularly a very high-resolution device.

    INL can be (and usually is) derived from DNL, and in fact the shape of the INL curve often provides insight in to a converter's dynamic performance. A bow contributes even-order distortion, a sinusoidal shape odd-order, etc.

    To head at least somewhat back on-topic, (time) jitter matters only in the presence of a varying signal. If the sampling time varies when there is no signal, or a d.c. (static) signal, jitter does not matter because it does not change the value of the sample. (Other error sources may, natch.) A constant jitter level may be more noticeable at lower signal levels as the error is a bigger fraction of the signal; otoh, the signal is also using fewer bits so there's a trade. I'm still working on the Jitter 101 thread...
    Don Herman
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  9. #99
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    Quote Originally Posted by DonH50 View Post
    ..jitter matters only in the presence of a varying signal.
    This is worth repeating and something that has been implicit in all of my explanations. Jitter modulates other signals. By itself, it does nothing. So unlike noise which you can measure even with nothing playing, jitter requires the signal itself to create distortion. And since there are infinite varieties of signals, and infinite profiles of jitter, it is a hard concept to boil down to canned scenarios.

  10. #100
    Member Sponsor [Technical Expert] DonH50's Avatar
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    Amir, you posted whilst I was typing. I'd like to offer a couple of quickies:

    Random jitter does not create harmonic distortion; it creates spurs in the response but these are somewhat randomly related to the signal. Deterministic jitter will create harmonic distortion terms.

    Quantization noise is not harmonic distortion of the signal, but rather more like, well, noise! It sounds worse than thermal noise because it is not truly white noise and there is a relationship to the signal. INL can (and does) create harmonics.

    And yeah, thinking of a good set of test cases to show the impact of jitter still has me cogitating....
    Don Herman
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