ABX testing lossy compressed audio over Bluetooth 2016-11-20 05:31:37 I had always been under the assumption, that recompressing lossy audio using another codec would cause noticeable artifacts that could be picked up in an ABX test. This belief came from reading various forum posts over the years (as well as the big warning foobar2000 pops up about converting from one lossy format to another.So, with the knowledge of lossy music transparency, I set out to ABX lossy vs lossles music over Bluetooth.Here's how I set things up.I bought one of these: http://www.xmpow.com/car-accessories/car-stereo-receiver/mpow-streambot-mini-bluetooth-4-0-receiver-a2dp-wireless-adapter-mbr4.htmlI charged it up, paired with my laptop, plugged my headphones into it and decided to ABX some tracks.I took a FLAC, and converted it to MP3 and AAC. In the middle of this ABX test, I realized that A2DP compresses audio, since Bluetooth bandwith is limited, and some Bluetooth chips have AAC and MP3 encoding/decoding in them. So I was concerned that my adapter was passing through the AAC or MP3 file without recompressing it. The specs for this device do not say what codecs it supports natively, so I didn't think I could do a valid test using either of these files.So, I decided to make an ogg file, at 256K, since I don't know of any Bluetooth chip that natively supports Ogg Vorbis.I then proceeded to ABX the original FLAC and the Ogg Vorbis file, under the belief that both files will get compressed using SBC or any other codec supported by the chip.I did an ABX on one file and came up with this result:Code: [Select]foo_abx 2.0.2 reportfoobar2000 v1.3.102016-11-20 00:12:52File A: 01 Cracklin' Rosie.flacSHA1: 02c014523ef42f869952be67b8c445abeaadbfc4Gain adjustment: -2.18 dBFile B: 01 Cracklin' Rosie.oggSHA1: b3fdaa425e02a7fafaa6621ee47c9da406f74a7eGain adjustment: -2.17 dBOutput:DS : Primary Sound DriverCrossfading: NO00:12:52 : Test started.00:13:46 : 01/0100:14:28 : 02/0200:14:51 : 02/0300:15:19 : 03/0400:16:09 : 03/0500:16:29 : 03/0600:16:50 : 03/0700:17:07 : 04/0800:17:07 : Test finished. ---------- Total: 4/8Probability that you were guessing: 63.7% -- signature -- 4478484a14daa7e38bf82fe0c496ae0e8714fa5eSo, it appears compressing a lossy file once isn't nearly as big a deal as the Internet made it out to be.Does anyone see any flaws with what I did here, other than not listening to every track all the way through?If someone can recommend a song that would be more likely to produce artifacts when recompressed, I'd be more than willing to try it.