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SiS 7012


vendor Silicon Integrated Systems
product 7012
interface Intel ICH, chip on ECS 755-A2 motherboard
duplex full
channels 2
resolution 16 bits
max rate 48 Ksample/sec
chipset SI7012
codec Realtek ALC655 rev 0
operating system Fedora core3 Linux x86_64 2.6.12-1
driver intel8x0 ALSA 1.0.9rc2
buffer size input 64 KB, output 64 KB
test date Aug 30 2005
notes Very strong DC offset at -35 dB.  Strange fragment drops every 600 seconds.  Set the Tone Generator's digital gain to -5 dB for 0.24 bits more of ENOB. 


This card is part of the Full Duplex DAQ comparison survey.

 
Sample Rate
The sample rate on DAQ cards is not a fixed absolute constant.  Like time, it fluctuates, and it is difficult to measure accurately.  Sometimes there are relationships between the input and output sample rates that can reveal interesting details about the inner working machinery.

The following table of measurements use a technique described in the sample rate stability application note. The rate column is the sample rate value that the collection hardware is programmed to.  The in/out rate and in/out error columns are absolute measurements of the ADC / DAC clock.  The loop error column uses a tone generator loopback method for a high accuracy measurement of the relative difference between the ADC and the DAC clocks.  The three error PPM columns are theoretically related by the formula: "in_error - out_error = loop_error"

rate in rate out rate in error out error loop error
4000 4010.977 4010.979 +2744.25 PPM +2744.75 PPM +110.6347 PPM *
5510 5506.098 5506.099 -708.167 -707.985 PPM -42.7455 PPM *
8000 8001.051 8001.056 +131.375 PPM +132.000 PPM +235.0659 PPM *
11025 11012.20 11012.22 -1161.0 PPM -1159.2 PPM -42.2645 PPM *
12000 12001.58 12001.59 +131.67 PPM +132.50 PPM +0.0000 PPM
16000 16002.11 16002.15 +131.88 PPM +134.38 PPM -36.9851 PPM *
22050 22024.38 22024.41 -1161.9 PPM -1160.5 PPM -19.3253 PPM *
24000 24003.16 24003.18 +131.67 PPM +132.50 PPM +0.0000 PPM
32000 32004.15 32004.23 +129.69 PPM +132.19 PPM +2.8044 PPM *
44100 44048.83 44048.86 -1160.3 PPM -1159.6 PPM +1.7196 PPM *
48000  48006.40  48006.42  +133.33 PPM  +132.75 PPM  +0.0000 PPM 

The "*" signifies a very noisy spectrum which probably makes the loop error measurement invalid. 

Below is the plot for the 22050 sample rate which shows a nice clean convergence.  All of the SiS 7012's sample rates display this respective shape and behavior.  This signifies the intel8x0 driver is handling the fragment interrupts properly.



The precision with the in rate and out rate isn't as good as usual because either Fedora core3 or the audio driver are causing a fragment drop every 600 seconds.

 
Frequency Domain
The sound card's input and output jacks are connected with a short external cable and run in full duplex mode.  This is a loopback test and baudline's tone generator is the signal source.  Distortion, noise floor, filter response, and inter channel crosstalk are the frequency domain measurements of interest in this section. 

The signal test sources are a pure sine wave, a linear sine sweep, and WGN.  The sine wave is used for the distortions and crosstalk measurements.  The linear sine sweep and WGN are used for the filter characterization measurement.  Both are an application of the swept sine vs. WGN technique and are equivalent measures of the frequency response. 

Since spectral performance is a function of sample rate, each of the sound card's native rates will be tested.  The highest sample rate is usually the cleanest and this is advantageous because it allows the isolated testing of the ADC and the DAC.  The matched, source, and sink sample rate combinations are described below.

matched
The input and output sample rates are the same.  This combination tests the performance of both the ADC and the DAC in a matched mode of operation.  The linear sine sweep signal in the left spectrogram display and the WGN (orange) in the Average window characterize the in-band filter response.  The sine wave (green) in the Average window is used for distortion and crosstalk measurements.  The sine leakage (purple) is used for crosstalk measurement

source
The sample rate of the input (sink) is the card's highest clean rate.  This combination tests the performance of the DAC.  The linear sine sweep signal in the middle spectrogram display characterizes the DAC filter response.  The position of the pass-band and the stop-band filter transition is defined by the Nyquist frequency of the DAC.  The noise floor (purple) is the Average collection of a silent channel.

sink
The sample rate of the output (source) is the card's highest clean rate.  This combination tests the performance of the ADC.  The linear sine sweep signal in the rightmost spectrogram display and the orange curve in the Average window below it characterize the ADC filter response.  The position of both the pass-band and the stop-band filter transition is defined by time in the spectrogram and by folded frequency in the Average window.  The orange Average curve represents the pass-band while the cyan curve is a folded representation of the stop-band ADC filter response.  The noise floor (purple) is the Average collection of a silent channel.

The naming convention for the columns below is (DAC -> ADC) where DAC represents the source sample rate and ADC represents the sink sample rate. 


matched
source (DAC)
sink (ADC)
4000 -> 4000 4000 -> 48000 48000 -> 4000

The wideband pulses in the 4000 source spectrogram sweep has a 0.382 second period (1528 samples).

5510 -> 5510 5510 -> 48000 48000 -> 5510

The wideband pulses in the 5510 source spectrogram sweep has a 0.411 second period (2265 samples).

8000 -> 8000 8000 -> 48000 48000 -> 8000

The wideband pulses in the 8000 source spectrogram sweep has a 0.128 second period (1024 samples).

11025 -> 11025 11025 -> 48000 48000 -> 11025

The wideband pulses in the 11025 source spectrogram sweep has a 0.206 second period (2271 samples).

12000 -> 12000 12000 -> 48000 48000 -> 12000


16000 -> 16000 16000 -> 48000 48000 -> 16000

The wideband pulses in the 16000 source spectrogram sweep has a 0.128 second period (2048 samples).

22050 -> 22050 22050 -> 48000 48000 -> 22050


24000 -> 24000 24000 -> 48000 48000 -> 24000


32000 -> 32000 32000 -> 48000 48000 -> 32000

The wideband pulses in the 32000 source spectrogram sweep has a 0.128 second period (4096 samples).

44100 -> 44100 44100 -> 48000 48000 -> 44100


48000 -> 48000  
 

The orange WGN curve shows a very odd looking filter.  Also notice the intersecting lines in the spectrogram display.



distortion
The following table of measurements were made using the technique described in the sine distortion application note.  It is a full duplex test that uses a loopback of the tone generator to measure the various distortion parameters.  The stereo crosstalk column is a measure of channel leakage that uses a sine wave channel and a silent channel as the signal sources.

rate SNR THD SINAD ENOB SFDR crosstalk
4000 +39.79 dB -47.22 dB +39.07 dB +6.196 bits +45.19 dB -92.07 dB *
5510 +40.28 dB -50.51 dB +39.89 dB +6.332 bits +46.24 dB -91.54 dB *
8000 +37.46 dB -47.20 dB +37.02 dB +5.856 bits +41.28 dB -90.51 dB *
11025 +30.96 dB -50.15 dB +33.85 dB +5.331 bits +38.28 dB -92.74 dB *
12000 +70.81 dB -75.33 dB +69.50 dB +11.251 bits +76.78 dB -90.37 dB
16000 +51.47 dB -54.32 dB +49.66 dB +7.955 bits +55.81 dB -90.39 dB *
22050 +25.85 dB -39.91 dB +25.68 dB +3.973 bits +31.61 dB -90.72 dB *
24000 +70.00 dB -71.93 dB +67.85 dB +10.977 bits +74.82 dB -89.03 dB
32000 +23.62 dB -42.89 dB +23.57 dB +3.623 bits +23.62 dB -88.31 dB *
44100 +18.46 dB -29.17 dB +18.11 dB +2.715 bits +22.80 dB -86.51 dB
48000  +69.84 dB  -70.95 dB  +67.35 dB  +10.894 bits  +72.69 dB  -86.33 dB 

The "*" symbol signifies the distortion metrics for that particular sample rate are invalid due to spectral damage caused by wideband noise pulses.


All the rates except 12000, 24000, and 48000 suffer from some major spectral flaws.  The flaws are in the form of wideband pulse, crosshatch aliasing, folded aliasing, or a combination of all three.  The 12000, 24000, and 48000 have the best distortion values.

The filters on the playback DAC side are very poor with minimal rejection.  The filters on the record ADC side are practically nonexistent.

The spectrogram sweeps and the average spectrum plots look surprisingly similar to the VIA 8235 audio device which also uses a Realtek codec.

 
Quantization
A white Gaussian noise signal source was generated and captured in full duplex loopback fashion at each of the standard sample rates.  The Histogram plots below show a unique sample distribution that is dependent on sample rate.

The purple and green Gaussian histogram shapes are slightly separated because of a small inter channel difference of their DC offsets.

4000, 5510, 8000, 11025, 16000, 22050

A nice Gaussian shaped bell curve with a wide notch cut down the center line.

12000

Like the above histogram but with the top points smoothed down and some extra lumps added.

24000

Like the previous histograms but the two horns are squeezed together slightly and the addition of a third peak in the center where the cutout notch was.

32000

This looks exactly like the 24000 histogram but with the new center peak removed.

44100

A slightly melted version of the 24000 histogram.

48000

Looks more like a standard Gaussian curve but with a slight center peak.

The progression of the center line notch as the sample rate increases is interesting.  Not sure what this says about the resampling algorithm but something unusual is at work.

 
Channel Delay
A sine wave signal was generated and captured in full duplex loopback mode.  The time domain response was observed with the Waveform window where the green curve represents the left channel and the purple curve represents the right channel. 



The SiS 7012 chipset has a zero sample inter channel delay.

 
Analysis
The 12000, 24000, and 48000 rates have a zero PPM sample rate loop error, clean spectrum / spectrogram sweeps, and low distortion.  Unfortunately the 12000 rate lacks an ADC filter and the 24000 rate has a very poor ADC filter with only -20 dB of rejection.

The large sample rate PPM in/out errors seem to correlate well with the crosshatch aliasing found on the sink ADC side for the 4000, 5510, 11025, 22050, and 44100 rates.  Not sure what the DSP connection is but it probably has to do with the flawed algorithm that is performing the sample rate conversion.

No correlation between the unusual histogram quantization shapes and spectral performance can be made.

 
Conclusion
The filters on the playback DAC side are very poor with minimal rejection.  The filters on the record ADC side are practically nonexistent.

Only use the 48000 sample rate with the SiS 7012 chipset.  All of the other sample rates suffer from severe spectral damage.  Audio playback at 44100 is not recommended with this chip.

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