Hi Matthias, thanks for your reply.
The manual's entry is the same since 10 years or so…
Why publish info that you know is 10 years out of date?
The crystal used in the DAC is referred to as the lowest jitter crystal currently available, outperforming the famous Crystek ones.
If you’re using today’s latest crystal, why are the specs still the same as 10 years ago?
...it refers to clock jitter that can be measured on external outputs like the wordclock one with a standard Digital Sampling Oscilloscope.
Neither the ADI-2 DAC or ADI-2 PRO actually have any external wordclock output.
PicoQuant, Keysight, Standford Research and others do make time interval counters accurate down into the small picosecond ranges. Surely there is a way to measure the internal performance to better precision than <1 nanosecond.
If you’re only measuring to approx 1 nanosecond resolution at the outputs, how can you quantify subtle improvements to the design like the “SteadyClock FS” enhancements?
Surely you must also need to measure with much higher precision to assess any improvement the femtosecond clock makes? How else can you know if your “SteadyClock FS” is operating within its target spec or not? Why aren’t you publishing those figures?
Still we will not enter this useless number throwing game.
If quoting the crystal clock jitter specs is a “useless number throwing game” why are the industry’s most respected converter companies like Prism Sound, dCS, Antelope, Mytek, Lavry, Apogee, Benchmark, Lynx, Black Lion, Forssell Technologies, Crane Song, etc., all treating it seriously?
Neither ours nor Crystek give a single jitter number (which has no meaning as it doesn't tell where and how it was measured), but a diagram of jitter over frequency in dBc, with values far below -100 dBc
Okay, so print the graphs as well as publish the figures.
Page 75 of ADI-2 Pro manual has a jitter graph at half the Nyquist freq of 11.025kHz, sampled at 44.1kHz, but considering the converter goes up to 768kHz sampling rate, the proportional impact of that jitter relative to the 768kHz sample period and its waveform reconstruction would be made over 16 or 17 times more severe!
Futhermore you’re claiming an audio frequency response up to 180kHz @ -3dB for A/D and 115kHz for the D/A, which means a single fullscale cycle of a wave at that frequency must race across the 24 bit quantisation levels at a much faster pace because of it’s shorter duration at higher frequency than your graphs’s 11.025kHz wave, so the number of discrete quantisation levels covered during each sample’s timing jitter uncertainty period is a whole lot more, at least 10 times greater, as well, which will effectively lower the precision resolution in quantisation bits at those higher frequencies. Certainly not able to define the signal amplitude to the full 24 bit depth at those frequencies. The lower bits would be just erroneous random data. Hence the picosecond jitter value is of importance to know potentially how far the converter can resolve or reconstruct the audio signal.
The fact it produces sidebands on a freq domain graph is just another way of viewing the same information.
If the crystal jitter figure is 0.7 picoseconds or something, that would be amazing, and would prove to me mathematically that the converter clock can resolve tighter timing steps than 24 bit quantisation level steps over a fullscale 20kHz audio speed bandwidth, which is more than good enough for me – I can’t hear to 180kHz anyway. But given a specsheet jitter figure of 800 picoseconds only, and no further information, I’m left guessing.
More info is not available from RME at this time, sorry.
That’s a pity because I was hoping to purchase 3 of these. (6 channels for a 3-way digitally FIR processed tri-amped monitor system.)
I'm quite willing to believe the RME ADI-2 DAC really is a fantastic product, and most reviews I’ve read online seem to agree. I don't own it and have never heard it myself. I’m not criticising or doubting the actual hardware is top notch, I’m just asking for better explanation of the specsheet figures, because they appear to be in contradiction to the real nature of the product.
Daniel Fuchs wrote:
The jitter value quoted by Mytek is only called "internal jitter", and does not refer to external sync and actual conversion. No other (comparable) figures are provided.
This is why I’m asking RME for their comparable figure for “internal clock jitter” if that’s how you prefer to define it. So I as a customer can make a fair comparison. How does it compare to the 0.82 picoseconds of Mytek Brooklyn, or the calculated 0.88 picosconds of Antelope Pure2.
I understand that a few inches further down the copper tracks on the circuit board it may measure worse, and by the time it’s passed through buffers and a consumer S/PDIF optical interface, it will be degraded further, but we’ve got to be able to compare on a level playing field to start with, so let’s start with the internal crystal clock jitter. Do you have this figure anywhere?