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panson_hk 13th September 2012 06:22 AM

WinAudioMLS, A Powerful analyzer
 
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I recently purchased a non-commerical version of WinAudioMLS. It is a very powerful tool. In order to support this powerful tool, a decent audio interface is needed. We can buy off-the-shelf USB audio interface supporting 24-bit, 192 kHz. Not all of them give you best analog performance.

Here is my plan: USBStreamer from miniDSP + home made high-performance analog front. USBStreamer is based on XMOS USB audio solution. It supports 24-bit, 192 kHz streaming. Driver of USBStreamer supports ASIO. High-performance 24-bit, 192 kHz ADCs are available from Digikey, Mouser, etc. We can add opamp signal conditioning circuit and attenuator to have a complete analog front end. Currently, I using WM8788 for evaluation. Here is WinAudioMLS and USBStreamer running at 96 kHz sample frequency. Input of WM8788 is connected to a 1 kHz low-distortion signal source.

FFT shows harmonics of 60 Hz mains. 8 kHz and 16 kHz are external interference.

panson_hk 13th September 2012 08:55 AM

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I set the USBStreamer in loopback mode where output ch1&2 connected to input ch1&2. Hence, we can test the system performance limit.

Red curve is standard FFT and Cyan curve is 64-bit FFT. SNR improves significant with 64-bit computation.

1audio 15th September 2012 01:59 PM

That looks like digital loopback. No analog system will get that good that I have seen. The Minidsp stuff is well done.

panson_hk 15th September 2012 11:11 PM

Yes, it is loopback at I2S in/out of USBStreamer. It can be used as reference to evaluate attached analog performance.

Boscoe 23rd September 2012 09:24 PM

What are the distortion figures?

skidave 25th September 2012 09:33 PM

As Boscoe said, what are the distortion figures. Did you try his signal generator with this software as well (the free one)?

panson_hk 26th September 2012 03:20 AM

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Quote:

Originally Posted by Boscoe (Post 3176241)
What are the distortion figures?

Here is THD of loopback.

Right figure: default setting, THD+N = 0.0077%, THD = 0.0027%
Left figure: 64-bit FFT, THD+N = 0.0008 %, THD = 0.0000 %

panson_hk 26th September 2012 03:30 AM

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Quote:

Originally Posted by skidave (Post 3178935)
As Boscoe said, what are the distortion figures. Did you try his signal generator with this software as well (the free one)?

The free one seems to have poor performance as shown in the figure. It has much higher noise floor and frequency offset.

Frequency was set to 777 Hz.

panson_hk 26th September 2012 03:50 AM

Windows function affects THD result
 
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The choice of FFT window function affects the THD result.

Left: THD+N is -105 dB for Blackman window.
Right: THD+N is -144 dB for Rife-Vincent window.

Both are with 64-bit FFT enabled and looback.

panson_hk 26th September 2012 03:52 AM

I am working on a front-end board for this test setup.


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