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RE: Does ASRC (upsampling) hurt pass band ripple in general?

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Dave_K

In Reply to: RE: Does ASRC (upsampling) hurt pass band ripple in general? posted by dave789 on July 24, 2015 at 05:03:31

A reasonable implementation of ASRC should not produce FR variations all the way down to 350 Hz as shown. Nor the channel mismatch shown. It could be coming from the analog preamp section. It might also be an artifact of the measurement setup, e.g. a ground loop.

Follow Ups:

RE: Does ASRC (upsampling) hurt pass band ripple in general? - dave789 06:55:05 07/24/15 (8)
Benchmark DAC1 HDR.

See whether 4kHz is emphsised or de-emphasised compared to the adjacent frequencies. One picture is with 44.1kHz sample rate digital signal input, the other with 55kHz sample rate digital signal input.

The ripple can be said to be small in some sense, but big compared to the ripple of probably-non-up-sampling DAC in iPhone.
- I'm not convinced ASRC is the culprit though - Dave_K 04:27:05 07/26/15 (6)
  Especially for that bit of "noise" shown in the response of the Cambridge DAC in the 350-2000 Hz range.
  
  I don't see why the digital filter used in the upsampling process would be flat in the pass-band when the output sample rate is a power of 2 multiple of the input sample rate (oversampling), but then have ripple in the pass-band when the output rate is a non-integer multiple of the input rate (ASRC). It could be true, but I just don't understand what digital filter design method would produce that and why that method would only be used in the ASRC case.
  
  I don't think we can conclude much from 3 samples, especially considering the iPhone is measured differently than the Cambridge DacMagic and the Benchmark DAC1. The iPhone has no power supply connection. Inherently, it has a floating ground, and in the test setup it's ground reference is provided by the probe of the audio analyzer. So there's no possibility of ground loops like there is with the other DACs. Also, the iPhone doesn't require an external transport. The others must have a transport included in the test setup. Finally, all three products have different implementations of volume control.
  - passband ripple specs in +/- dB - dave789 06:56:42 07/26/15 (5)
    ASRC (upsampling)
    CS8422: 0.05
    SRC4392: 0.008
    
    DAC chip (oversampling)
    PCM1796: 0.0002 (for sharp roll off)
    CS4396: 0.0001 (for 32, 44.1, 48)
    WM8742: 0.000058
    
    Edits: 07/26/15 07/26/15
    - So? - Dave_K 10:03:35 07/26/15 (4)
      Are any of these used by the Cambridge DacMagic and Benchmark DAC1 HDR?
      - RE: So? - dave789 11:03:19 07/26/15 (3)
        
        In Reply to: RE: So? posted by Dave_K on July 26, 2015 at 10:03:35
        
        Yes, of course.
        
        DacMagic 100 has WM8742: 0.000058.
        
        Benchmark DAC1 HDR has SRC4392: 0.008.
        
        By the way, DacMagic and DacMagic 100 are very different. The old DacMagic and the current DacMagic Plus use upsampling, but the current DacMAgic 100 does not use upsampling.
        
        Benchmark DAC1 has AD1896, and Cambridge DacMagic Plus has Anagram upsampler - Dave_K 11:31:49 07/26/15 (2)
        
        In Reply to: RE: So? posted by dave789 on July 26, 2015 at 11:03:19
        
        Benchmark DAC2 has SRC4392 and Sabre DAC. Benchmark DAC1 used AD1896 SRC and AD1853 DAC.
        
        I was less sure about the Cambridge, but a little Googling revealed that the original DacMagic and DacMagic Plus have an Anagram Technologies sample rate converter (ATF in the original and ATF2 in the Plus).
        
        Pass-band ripple spec on the AD1896 is +/- 0.016 dB, but the ripple pattern looks pretty conventional, typical of an elliptic filter, not like the one you posted earlier. See the pass-band ripple plot (TPC35) on page 13 of the data sheet. Link below.
        
        http://www.analog.com/media/en/technical-documentation/data- (Open in New Window)
        
        RE: Benchmark DAC1 has AD1896, and Cambridge DacMagic Plus has Anagram upsampler - dave789 20:09:24 07/26/15 (1)
        
        In Reply to: RE: Benchmark DAC1 has AD1896, and Cambridge DacMagic Plus has Anagram upsampler posted by Dave_K on July 26, 2015 at 11:31:49
        
        In the graph you mentioned, the horizontal axis is linear scale. The measurement graph I linked is octave scale (logarithmic).
        
        RE: Benchmark DAC1 has AD1896, and Cambridge DacMagic Plus has Anagram upsampler - Dave_K 02:28:36 07/27/15 (0)
        
        In Reply to: RE: Benchmark DAC1 has AD1896, and Cambridge DacMagic Plus has Anagram upsampler posted by dave789 on July 26, 2015 at 20:09:24
        
        The location and spacing of the peaks in the ripple pattern aren't the same even accounting for scale. More importantly, the roll-off in the Ken Rockwell plots starts a lot earlier and with a shallow slope. The AD1896 data sheet shows the classic "brick wall" filter response whereas the Ken Rockwell plot shows a response down by 0.05 dB at 10 KHz and 0.2 dB down at 20 KHz. The only thing that really matches is the magnitude of the ripple. There might be a connection there, but it's no smoking gun.
        
        Besides all that, I don't think we've connected this to the use of ASRC. There's no reason to think that ASRC lends itself to using a particular filter design function. If you want no pass-band ripple and can tolerate a wider transition band, you use a Cheby II function (or even Butterworth). If you want the narrowest transition band, you use an Elliptic function. The different filter performance metrics can be traded off easily with most filter design software. I can't think of any reason why these basic filter design tradeoffs would be dependent on the output sample rate of an interpolation filter.
- RE: Does ASRC (upsampling) hurt pass band ripple in general? - beautox 14:24:16 07/25/15 (0)
  Don't trust Ken Rockwell, especially anything he says about audio.

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