Listening with your eyes? How to read graphs.

[Bruce B]

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 “look” at the FFT and spectrogram and determine it’s an upsampled file.
What I’m going to try to do today is to teach everyone how to read these files and ways to determine if it’s really hi-rez or not!
So many times I’ve seen reviews of SACDs touting its sonority until someone determines that it is just an upsampled file and all of a sudden it doesn’t sound good anymore. What a crock!
O’kay… let’s start off with an easy one. We all know that Redbook CD’s 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 SACD’s to me to get the DSD information off of them for download and look what I find. A definitive, easy to detect, upsampled SACD.

[Bruce B]

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 it’s hi-rez? The below photo shows that phenomenon.

[Bruce B]

Now what happens if you take an FFT of a whole album and it shows you this.

[Bruce B]

This is a picture of the whole album. But what if a label doesn’t 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.

[Bruce B]

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?
I’ll post more about this rant later after some discussion!

[garylkoh]

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.

[tomelex]

Are you still with me?
I’ll post more about this rant later after some discussion!

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