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Thread: Listening with your eyes? How to read graphs.

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    Listening with your eyes? How to read graphs.

    Listen with your ears, not your eyes!
    This may seem funny, but for the past 2-3 years I spend hours replying to emails from angry customers that have downloaded files from HDtracks and use inferior tools to ďlookĒ at the FFT and spectrogram and determine itís an upsampled file.
    What Iím going to try to do today is to teach everyone how to read these files and ways to determine if itís really hi-rez or not!
    So many times Iíve seen reviews of SACDs touting its sonority until someone determines that it is just an upsampled file and all of a sudden it doesnít sound good anymore. What a crock!
    OíkayÖ letís start off with an easy one. We all know that Redbook CDís are 16/44.1. A few major labels thought they could pull a fast one and reissue their complete catalog into this new format. Easy money, right? They just take these 24/44.1 files and convert them to DSD and produce SACDs of the same material. Unfortunately they send the SACDís to me to get the DSD information off of them for download and look what I find. A definitive, easy to detect, upsampled SACD.
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    Bruce A. Brown
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    Now on to a harder one! As you are well aware, DSD files contain high frequency noise if filters are not applied in the workstation. Some music contains very little content above 20k. DSD noise starts to creep in around 22k. What if the performance was a quiet one? The DSD noise will overpower the content above 20k. So how do you determine if itís hi-rez? The below photo shows that phenomenon.
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    Bruce A. Brown
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    Now what happens if you take an FFT of a whole album and it shows you this.
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    Bruce A. Brown
    Puget Sound Studios
    Stereomojo reviewer
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    This is a picture of the whole album. But what if a label doesnít have a high rez file of a particular song on the album? What you need to do then is a spectral analysis of the whole album. You can see below that tracks 4, 9, 12, 14, 17 and 19 are NOT hi-rez.
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    Bruce A. Brown
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    Are you still with me?
    We can throw more monkey wrenches into the mix. Let me put these scenarios out to you for discussion. Theoretically 24bit files have a dynamic range of 144dB. That means you need a software program that can go that low into the darkness. We use a program that can go down to -150dB.
    What if they upsampled a 16bit file? What happens to a redbook file that is upsampled to DSD and run through an analog console? How much noise do dither algorithms produce?
    Iíll post more about this rant later after some discussion!
    Bruce A. Brown
    Puget Sound Studios
    Stereomojo reviewer
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    Nice! Thanks for taking the time to do this, Bruce. It's not only the SACDs that can just be up-sampled Redbook, there are many DVD-A that are the same.

    For those of us who are just curious, the free software Audacity will also be able to do this spectrum analysis, but obviously more limited than the resources that Bruce can bring to bear.
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    Quote Originally Posted by garylkoh View Post
    Nice! Thanks for taking the time to do this, Bruce. It's not only the SACDs that can just be up-sampled Redbook, there are many DVD-A that are the same.

    For those of us who are just curious, the free software Audacity will also be able to do this spectrum analysis, but obviously more limited than the resources that Bruce can bring to bear.
    Unfortunately Gary, Audacity have been proven over at the CA forum to be unreliable and give false readings. That's what I mean about inferior tools in the hands of inexperienced people.

    Which brings me to yes, we have found quite a few DVD-A AND a handful of Blu-ray discs with upsampled files.
    Bruce A. Brown
    Puget Sound Studios
    Stereomojo reviewer
    Seattle, WA


    Even a blind squirrel gets a nut once in a while!

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    Quote Originally Posted by tomelex View Post
    Bruce, brilliant idea and post. Sorry, but, no I am not with you. For posts 4, I think you might tell us specifically what you see on the graph or spectrum,

    Post 4 did not readily pop out at me at first glance!

    Tom
    Post #2 dips down to 23k at approx -123dB. Now if this is a 24bit file, I would say this started out as a 48k file, since we know if it was a Redbook file, it wouldn't contain anything over 22.5k.

    Post #3 shows a dip at about 22.5k, but only at about -119dB before the DSD high-frequency content takes over. A way to look into this further is to make a considerable gain change in the file for the high frequency content to overcome the DSD artifact.

    Post #4 is a one hour timeline going across with the freq. content going vertical. Over on the left side you can follow 22.5k across the timeline and see where some tracks cut off at the frequency. Those are upsampled tracks within the file.
    Bruce A. Brown
    Puget Sound Studios
    Stereomojo reviewer
    Seattle, WA


    Even a blind squirrel gets a nut once in a while!

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    WBF Technical Expert (Speakers & Audio Equipment)/Member Sponsor [Technical Expert] garylkoh's Avatar
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    Quote Originally Posted by Bruce B View Post
    Unfortunately Gary, Audacity have been proven over at the CA forum to be unreliable and give false readings. That's what I mean about inferior tools in the hands of inexperienced people.

    Which brings me to yes, we have found quite a few DVD-A AND a handful of Blu-ray discs with upsampled files.
    Oh no. Does it also make bad recordings??
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    Genesis Advanced Technologies

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    Quote Originally Posted by garylkoh View Post
    Oh no. Does it also make bad recordings??
    I haven't heard any bad things about that part..... I think you're safe!
    Bruce A. Brown
    Puget Sound Studios
    Stereomojo reviewer
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    Even a blind squirrel gets a nut once in a while!

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