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dr_z

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Everything posted by dr_z

  1. Nice catch & thanks! The title was incorrect (variable error in my makefile grabbed the bit depth from the last of the J-test files) -- I'll get a corrected copy uploaded ASAP...
  2. A while back, over beer & conversation, a colleague and I thought it would be fun to write a couple of test files in MATLAB for our stereo systems. We ended up dumping the results to WAV files and burning them to CD-R -- next thing you know we had our own little Test CD. A few years/beers later, I re-wrote same and added to them when I decided it was time to move on in my research from MATLAB to Python... now that "Test CD" has morphed into a collection of files (both PCM encoded as FLAC and DSD as DSF) packaged as an album suitable for use with a music server. There's even an accompanying booklet in which I attempt to explain in some detail the individual tracks. The entire thing is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 (CC BY-NC-SA 4.0) International License, so feel free to use it under those terms. Perhaps you’ll find it interesting and of some use, if not amusement. Here is the CD booklet for people to browse through. It's included with the complete CD download below as well. Download Link - https://audiophile.style/b (4.8MB PDF) Here is the complete CD download containing the booklet, Disc 1 for PCM files and Disc 2 for DSD files. Download Link - https://audiophile.style/z (380MB ZIP) The following is the introductory paragraph contained on page one of the booklet. Dr. Z’s Test CD This PDF document serves as the liner notes (or ”booklet”) for Dr. Z’s Test CD, which is really just a collection of 24/96 files1 in the FLAC format2 and not a physical disc at all. But back in the day, my colleague Prof. John V. Olson and I used to dump files like these in WAV format onto a CD-R for use at home – such were the halcyon days before ”computer audio” was a household thing – hence; for historically sentimental reasons, a Test CD. That said, the ”disc” was authored for system evaluation and set-up, and is therefore not recommended for an enjoyable listening session. You may think that there are some typical test files missing or notice that there isn’t much in the way of traditional musical content – as to the former, a dedicated ”burn-in” track is pointless and the intent was listening, not to write tracks for use with an oscilloscope to directly test electronic components (perhaps a Test CD 2?);3 as for the latter, nothing musical is really missing, since that’s what your collection is for, isn’t it? This ensemble of tracks is primarily designed for testing and evaluation of loudspeaker placement, system setup, room characteristics and overall performance while ensconced in your favorite listening chair. You can use it with headphones, too, but with such devices you would be testing more for your hearing sensitivity or capsule isolation. Headphones are sufficiently unique beasts in their non-flat responses and they don’t really interact with the listening room. Bottom line: this is nothing more than a work of computational-audiphiliac Onanism. I’m trained as a physicist, but do a fair amount of statistical signal processing in my work,4 particularly on digital records of infrasound generated from natural and anthropogenic sources (and in a previous life, of ground-based magnetometer data from the interaction of the solar wind with Earth’s high-latitude magnetic field). But long before that I just really enjoyed listening to recorded music and thinking about the equipment that made that possible. That fascination has remained a strong and continuous thread, making for a lifelong pursuit; this work is therefore but an ex- tension of it: to learn more about the digital aspects of music reproduction, as well as how we perceive that reproduction in real-world listening spaces. There are numerous other very fine Test CDs out there, so why make my own? I tell students that using a ”black box” is all well and good – I drive a truck and certainly wouldn’t want to build one – but from time to time you get more out of making your own box to better understand what’s inside and how it works. In particular, the best way to make sense of data is often to ”play” with it (using various digital signal processing tools), so what better playground than a project like this? I get to make the very data I’m about to play with! This particular project all started a few years ago over a beer and conversation... a few years/beers later and this is what I came up with. Perhaps you’ll find it interesting and of some use, if not amusement. 1. Several alternative bit depths and sample rates are used in a few of the tracks to test for such things; all the other tracks were rendered at 24-bit/96 kHz resolution. 2. Beginning with ver. 1.1, a second ”disc” of DSD files in the DSF format was included. 3. In ver. 1.1.2, some of those electro-analytical type files were added at Track. 4. To be honest, I do more managing scientists and translating science to other non-techncial managers than actual science these days, c’est la vie.
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