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Xonar D1 measurements

Discussion in 'Computer Audio' started by stv014, Sep 30, 2012.
  1. stv014
    The following article shows the results of a farily extensive test of the Xonar D1 PCI sound card. In my opinion, this card is very good value for its low (less than $100) cost, and can - if used in a machine where interference is not an issue - even compete with the ODAC. It is also available in a PCIe version (Xonar DX), which I did not test, but would hopefully perform similarly.

    Basic parameters (input/output levels and impedances)

    On the front channel output, I measured 1.934 Vrms (left) and 1.938 Vrms (right) voltage playing a 1 kHz sine wave at 0 dBFS and maximum volume. These values may vary slightly (probably within 1%) as a result of random manufacturing variation, and the DMM used also adds a potential +/- 1% inaccuracy. In any case, the card outputs slightly less than the specified 2 Vrms, but it is a relatively minor difference. The output impedance is about 100 Ω, which is not quite ideal for driving headphones, and also limits the maximum power output to less than 10 mW. The output is capacitor coupled (220 uF), and is driven by an NJM5532 op amp.
    The other channels - from the CS4362 6-channel DAC chip - output a slightly higher voltage, use much smaller (22 uF) coupling capacitors, and have only a few Ω of output impedance, but driving low impedance loads from these outputs results in significantly increased distortion.
    On the line input, a signal of about 2.0 Vrms is needed to reach the digital 0 dBFS level, but the distortion starts to increase at about -3 dBFS, reaching nearly 0.1 % with a full scale signal. The line input has a relatively low impedance of 3.8-3.9 kΩ.

    Test setup

    For recording, I used a Xonar Essence STX sound card in the same PC. This made it necessary to also use a differential amplifier described and tested here, otherwise grounding issues would have significantly degraded the result. The recording sample rate and resolution were always 192 kHz and 24-bit, although in some cases I resampled the files to a different rate using a high quality converter. The tests were run on a Linux OS, using ALSA hardware (hw:x,x) devices.
    The default testing conditions for the Xonar D1 (i.e. assume these parameters for all tests unless specified otherwise) were 44.1 kHz sample rate, 24-bit resolution, 5.4 kΩ load (the input of my differential amplifier without an additional low impedance load), full volume, 0 dBFS signal level, and "fast roll-off" DAC filter. All tests were performed on the front channel output of the card, not using the - generally worse quality - front panel jack.
    The tests have revealed that (at least my particular) Xonar D1 has an about 6.5 ppm "slower" clock than the Xonar STX. Of course, this value is subject to random manufacturing variations, but it should be plenty low enough not to be audible (it is musically equivalent to a pitch difference of ~0.011 cents). Although pitch accuracy is usually not even a problem in onboard audio.
    It is important to note that all these test results are the combination of the performance of all components used, therefore they cannot be fully reliable, even if they do show with reasonable confidence that the card is objectively fairly good (it is unlikely that both the playback and recording devices are significantly poor, and the errors almost perfectly cancel each other out). In particular, the following limitations of the recording equipment might need to be taken into account:
    - there is a small amount of bass roll-off, about -0.1 dB at 20 Hz
    - the ultrasonic range is also rolled off, but at 20 kHz the error should be within 0.1 dB
    - the total A-weighted noise floor (ADC + differential amplifier) is approximately -115.5 dBFS
    - there is some AC hum from the differential amplifier (less than -120 dBFS at 50 Hz)
    - while the distortion is fairly low, it is not insignificant compared to that of the DAC on the Xonar D1; it also increases at the highest audio frequencies. However, it should generally be within 0.001%, and at a not too high frequency and/or level, probably less
    - from about 50 kHz upwards, there is a significant "hump" in the noise floor, caused by noise shaping in the ADC
    - crosstalk is not low enough to allow for accurate measurement of this aspect of a high quality DAC, although it still well below any reasonable threshold of audibility
    - with the 22 Ω load, the (normalized) noise floor is much higher, because, due to the high output impedance, the input level to the ADC is lower by a ratio of 22 / (100 + 22), and the recording dynamic range is decreased accordingly
    Also keep in mind that the (especially noise) performance of a sound card can vary depending on the machine it is installed in. My PC is probably not a particularly noisy one, and the Xonar D1 is also in a PCI slot that is the farthest away from possible sources of interference.

    Frequency response

    fr.png     fr2.png
    Green: 44.1 kHz sample rate
    Red: 44.1 kHz, 22 Ω load
    Yellow: 96 kHz
    Blue: 44.1 kHz, slow roll-off DAC filter
    Note that there is a slight bass roll-off (about -0.1 dB at 20 Hz) from the A/D converter of the Xonar STX. The line input of the Xonar D1 has a similar roll-off, by the way. On the output, there is only a relatively significant bass roll-off (still only about 0.5 dB) when driving a low impedance load; this is caused by the 220 uF output capacitors.
    The graph on the right has a linear frequency scale, to better show the details of the high frequency response.
    Overall, the response is very flat, and should not be much of an issue in practice when using the card as a line level source.


    Blue: 22 Ω load, left to right
    Yellow: 22 Ω load, right to left
    Green: 5.4 kΩ load, left to right
    Red: 5.4 kΩ load, right to left
    Note: much of the crosstalk measured with a high impedance load at high frequency results from the recording gear, cables, and connectors. This is not easy to avoid, since with an output impedance of 100 Ω, it takes less than 10 pF capacitance between the channels to produce a graph like what is shown above. For the low impedance load, most of the crosstalk is caused by the ground impedance. In any case, none of this is close to actually being audible.

    THD vs. frequency

    Left: both channels driven, right: only one channel driven (the lower traces are cross-channel distortion, but in practice contain mostly noise)
    thdfreq1.png     thdfreq2.png
    Green / left: 44.1 kHz
    Red / left: 44.1 kHz, 22 Ω load
    Yellow / left: 96 kHz
    Blue / left: 44.1 kHz, -10 dBFS level (all the others are at 0 dBFS); this is in fact dominated by noise
    Green / right: 44.1 kHz, left channel driven
    Red / right: 44.1 kHz, right channel driven
    Blue / right: 44.1 kHz, 22 Ω load, left channel driven
    Yellow / right: 44.1 kHz, 22 Ω load, right channel driven
    Bandwidth: 50000 Hz
    Maximum order THD tested: 5
    As noted above, the cross-channel distortion graphs are mostly just noise, but with a low impedance load at high frequency, there is actually some distortion into the other channel. The analysis is more sensitive to noise at higher frequencies, because the window size used decreases with frequency. Also, with the 22 Ω load, the overall noise floor on the graphs is increased (this results from the dynamic range of the ADC not being fully used, rather than the output actually becoming more noisy).

    THD vs. level

    On all the graphs below, 1 on the horizontal scale means 0 dBFS level.
    Left: 44.1 kHz, 5.4 kΩ load; right: 44.1 kHz, 22 Ω load
    thdlvl1.png     thdlvl2.png
    Red: 60 Hz
    Yellow/Orange: 1000 Hz
    Green: 15000 Hz
    See also the comments above at THD vs. frequency.
    44.1 kHz, 22 Ω load, 11025 Hz signal
    This test used a trick (sample rate / 4 tone at 45 degrees phase) to create an output level of greater than 0 dBFS. Unlike many other DACs, the CS4398 apparently has headroom for such signals, and the card only starts to clip at about +2 dBFS (the Xonar STX would have hard clipping at exactly 0 dBFS).


    The vertical axis is the deviation from the correct level (it does show channel imbalance), so ideally you should see perfectly flat horizontal lines. At very low levels, the measurement is increasingly dominated by noise.
    level1.png     level2.png
    Blue/Red: left/right channel low level linearity
    Cyan/Yellow: left/right channel high level linearity (included as a level reference)
    Blue/Red: left/right channel high level linearity with zoomed in vertical scale
    The following graph shows performance with a low level signal under more difficult conditions. In addition to a 1201 Hz tone at -90 dBFS, the card has to play a large 431 Hz signal so that the overall peak amplitude is basically exactly 0 dBFS:
    Yellow: noise floor at 44.1 kHz
    Blue: test signals at 44.1 kHz
    Red: noise floor at 44.1 kHz, 22 Ω load
    Green: test signals at 44.1 kHz, 22 Ω load
    The graph is somewhat confusing because of all the noise, interference, and THD products of the high level signal, but there are no apparent THD or IMD products of the low level 1201 Hz tone, and it is at the correct -90 dBFS level, so the results are good.

    THD spectrum

    20 Hz (left) and 1 kHz (right) at 0 dBFS, red: 22 Ω load, yellow: 5.4 kΩ load. Note: the "humps" at integer multiples of 50 Hz are AC hum in the recording. The reason why they are not just narrow peaks is that the graph was created from the same sine sweep that was used in the THD vs. frequency analysis, with high quality dynamic resampling so that the frequency of the test tone itself remains constant.
    thd20.png     thd1000.png
    20 kHz; red: 96 kHz sample rate, green: 44.1 kHz sample rate, yellow: 44.1 kHz sample rate with 22 Ω load

    Intermodulation distortion

    60 Hz + 7000 Hz 4:1, 44.1 kHz sample rate (note the AC hum and its harmonics at multiples of 50 Hz, this comes from the recording gear, not the Xonar D1)
    smpte1.png     smpte2.png
    19000 Hz + 20000 Hz 1:1, 44.1 kHz sample rate
    Yellow: 5.4 kΩ load
    Red: 22 Ω load


    Left: 16-bit samples, right: 24-bit samples; both at 44.1 kHz sample rate
    jitter16.png     jitter24.png
    24-bit samples with system load (increased CPU+HDD+GPU activity)
    Yellow: the spectrum of the Jtest signal itself (i.e. zero jitter)
    Red: what was actually recorded, not driving a low impedance load
    The graphs were created using a 65536 sample Blackman-Harris window, and the 192 kHz recorded audio was resampled to 44.1 kHz, also correcting the slight sample rate mismatch between the DAC and ADC; this eliminated spurious "spread" from the windowing. The amplitude of the 11.025 kHz tone is -3 dBFS.

    DAC filter

    Spectrum of a 7-bit maximum length sequence at 44.1 kHz sample rate with the fast (yellow) and slow (red) roll-off DAC filters (fundamental frequency = 347.244 Hz):
    Impulse response, left: fast roll-off, right: slow roll-off (1.5 ms duration)
    ir_fast.png     ir_slow.png
    Phase response, and group delay vs. frequency, green: fast roll-off, yellow/orange: slow roll-off
    phase.png     gd.png
    It is too small to be visible on this graph, but there is also a slight delay between the channels, about 0.17 degrees of phase difference at 11025 Hz, or 43 ns delay. Neither the group-, nor the interchannel delay is high enough to be audible, though, I have seen the thresholds to be estimated at ~1 ms (it depends on the frequency, and is shortest in the midrange) and ~10 us, respectively.

    Noise, dynamic range, and THD+N at 1 kHz

    Sample rate Load System activity Signal level L RMS L A-wtd R RMS R A-wtd L THD+N RMS L THD+N A-wtd R THD+N RMS R THD+N A-wtd L Noise RMS L Noise A-wtd R Noise RMS R Noise A-wtd Dynamic range Compensated
    44.1k 5.4k No -60 -60.74 -60.74 -60.71 -60.71 -106.52 -109.36 -106.38 -109.30 -106.54 -109.38 -106.39 -109.33 108.60 109.81
    0 -0.74 -0.74 -0.71 -0.71 -103.88 -104.89 -103.92 -105.05 -105.98 -108.66 -105.85 -108.58
    44.1k 5.4k Yes -60 -60.74 -60.74 -60.71 -60.71 -106.54 -109.56 -106.45 -109.54 -106.55 -109.59 -106.46 -109.57 108.83 110.10
    0 -0.74 -0.74 -0.71 -0.71 -103.69 -104.62 -103.76 -104.81 -105.99 -108.81 -105.89 -108.77
    44.1k 22 No -60 -75.55 -75.55 -75.55 -75.55 -111.74 -115.04 -111.75 -115.10 -111.75 -115.06 -111.76 -115.12 99.51 109.77
    0 -15.56 -15.56 -15.56 -15.56 -109.81 -111.06 -109.68 -110.87 -111.68 -114.97 -111.67 -115.01
    48k 5.4k No -60 -60.74 -60.74 -60.71 -60.71 -110.07 -113.50 -109.87 -113.53 -110.08 -113.52 -109.89 -113.59 112.79 117.14
    0 -0.74 -0.74 -0.71 -0.71 -106.02 -106.65 -106.05 -106.85 -109.50 -112.51 -109.27 -112.47
    96k 5.4k No -60 -60.75 -60.75 -60.72 -60.72 -110.02 -113.50 -109.90 -113.51 -110.04 -113.53 -109.93 -113.58 112.78 117.11
    0 -0.74 -0.74 -0.72 -0.72 -105.79 -106.26 -105.94 -106.56 -109.56 -112.63 -109.44 -112.65

    System activity: if "yes", then there was intentionally high CPU, HDD, and GPU activity during the test. Oddly, this slightly reduced the noise level, but the test was performed at a different time, and factors like different temperature might have affected the results. In any case, the effect is minor, and listening to the recorded noise at greatly increased amplitude (by 80 dB) also reveals only a small amount of interference. On the other hand, the THD slightly increased, which again may have been the result of the system load, or other random factors. Of course, interference effects could be much more significant on other machines, especially ones with high end gaming GPUs or other high power components.
    Signal level: the level of the 1 kHz test tone in dBFS
    L RMS: unweighted total signal level measured relative to 2.0 Vrms, with a bandwidth of 5 Hz to 22 kHz
    L A-wtd: same as L RMS, but with the standard A-weighting filter applied
    R RMS, R A-wtd: same as above, but for the right channel
    L/R THD+N RMS/A-wtd: similar to above, but with a narrow notch filter applied at 1 kHz, to remove the test tone; to calculate actual THD+N values, subtract the 0 dBFS signal levels from the 0 dBFS THD+N levels
    L/R Noise RMS/A-wtd: similar to above, but with further narrow notch filters applied at harmonics of the 1 kHz tone, up to 11th order
    Dynamic range: this is calculated from the A-weighted THD+N at -60 dBFS, and the A-weighted total signal level at 0 dBFS; the signal power (10 ^ (dB_level / 10)) is summed on the two channels to get the overall levels
    Compensated: the approximately -115.5 dBFS A-weighted noise floor of the recording gear is subtracted from the THD+N levels used in the dynamic range calculations, in order to extrapolate the dynamic range of the DAC itself, and factor out noise from the ADC and differential amplifier; of course, these are not perfectly accurate, but should be an improvement over the raw dynamic range values
    What the results show, is that the card is apparently capable of the specified dynamic range (116 dB) and THD+N (-105 dB) at a sample rate that is a multiple of 48 kHz, but the noise performance degrades significantly at 44.1/88.2/176.4 kHz. This problem is common to Xonar family sound cards. However, the nearly 110 dB A-weighted dynamic range at 44.1 kHz is still very decent, and only slightly worse than that of the more expensive ODAC and Xonar STX (at the same sample rate).
    The CS4398 does not distort as much more at 96 kHz compared to 48 kHz as the PCM1792 used on the Xonar STX.
    Noise modulation is very low, increasing the signal level from -60 dBFS to 0 dBFS increased the noise floor by less than 1 dB. The Realtek ALC887 onboard audio I tested is much worse in this aspect, and some popular budget external DACs also have relatively high noise modulation.
    The line input of the Xonar D1 is not shown in the table above, but it can, in the best case, reproduce the -112 dBFS A-weighted noise floor claimed by the manufacturer.

    Useful links

    Stereophile Xonar Essence ST/STX measurements
    Xonar STX test report by ASUS (for comparison)
    OK, so what CAN I reliably measure from a PC soundcard ? (Sound Science forum thread)
    CS4398 datasheet
    Op amp distortion measurements
    xnor and reset like this.
  2. stv014
    Update: some graphs that displayed confusing units (like dB instead of ms, or Hz instead of dB) have been replaced. There is also a new phase response graph.
  3. ab initio
    Very thorough! :)

  4. mindbomb
    Thanks for the measurements. One thing I was wondering about was were these measurements taken with analog out in the xonar set to "2 speakers" or "headphones", and if the change makes any difference.
  5. stv014
    The test was not done on Windows, so these settings were not available. As far as I know, unlike the Xonar DG, the Xonar D1 does not have hardware support for switching between headphone and 2-speaker mode, the difference is only in the DSP (Dolby Headphone etc.) in the Windows driver.
  6. Apogee777
    I swapped out my slow dying X-Fi's (about 3 pci x-fi's over the years - old cards, cant use pci-e slot as my video card is too big) and had a pleasant non audiophile experience...
    As the output voltage is wrong as described in the reviews ^^ this caused an incredibly warm experience on my HD215's - from accuracy and well placed deep bass from the x-fi's, to a solid state amp-like sound with the Xonar D1
    admittedly i fiddled with the equaliser to achieve this, but increased bass on the x-fi would make the HD215's clip - the D1 does not. Rich warm bass with impressive soundstage combined with the dolby headphones dh-1 feature.
    Pity i don't have 2 pci-slots and be able to switch between the 2 soundcards :)
    Last edited: Aug 10, 2018

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