Since I always have trouble finding my CDs, I am considering to rip my whole CD collection to Ogg Vorbis or MP3. But to which format and bitrate? Everybody seems to agree on the fact that Ogg Vorbis sounds better for a given bitrate, but there aren't yet that many hardware players.
Since I would replace my CDs, transparency is the main requirement. People on the net declare that for full transparency, one would need at least ogg -q6 or mp3 at 300 kbps bitrate. I mostly listen to classical music, which is a bit sparsely represented in the various online tests.
I compared the compressed sound files to the original and tried to describe in what respect their sound differs (for some reason, this is seldom mentioned in online listening test reports), at least as far as I can reliably tell the difference in a blind ABX test. I found it easier to find sensitive spots in short fragments, instead of to switch back and forth during a whole track.
Apparently I have tin ears, because the encoders become transparent at bitrates far below the -q6 or 300 kbps that is mentioned by golden-ear listeners elsewhere, or my music taste is not demanding. (I do use a good headphone and a good sound card and my ears can still hear up to 20 kHz.) If someone knows how I can upgrade my ears, please tell me. :-)
As far as the encoders are not transparent, Ogg Vorbis and MP3 turn out to sound very different. Note that I hardly ever listen to MP3s and the like, so this may be a well-known fact for you. The MP3s tend to give annoying ringing artifacts, often strongly localized in certain music fragments. Ogg Vorbis, on the other hand, tends to distort the stereo image and create an overall hissing background and some coloration. Ogg Vorbis's distortions are much less annoying, because they are comparable to coloration by loudspeakers.
The stereo-image distortion is strongest in the choral and harpsichord solo recordings. Likely, different microphones were recording the same sound source in those cases, which results in strong phase differences between the left and right channels, which are apparently hard to encode in mid/side mode. I suspect that the other recordings mostly have an intensity stereo image as opposed to a phase image. Strangely enough, I didn't observe stereo imaging problems in the MP3s.
Enough said, here are the results.
I tweaked the --abr option such that the final average bitrate was with +/- 1.5 kbps the bitrate that I wanted. Lame wants to downsample at lower rates (below --abr 103), which my ABX test couldn't handle, so I forced a 44.1-kHz sample frequency. Maybe unfair to Lame at low bitrates, but that's life...
oggenc 1.0-7 -q xxx
I used oggenc simply with quality numbers.
Juan del Encina, Antonilla dees desposada Margaret Philpot (alt), Christopher Wilson(?) (lute) Hyperion CDA 66454 Comment: the lute in the original sounds as an artifact but isn't... mp3 80k: horrible buzzing (22.05 kHz resampled) mp3 96k: transparent ogg q0 (52.7k): some ringing ogg q1 (68.5k): transparent
J.S. Bach, Messe in B minor: Kyrie Eleison Ton Koopman, The Amsterdam Baroque Orchestra and Choir Erato 4509-98478-2 mp3 96k: strong ringing mp3 112k: audible mp3 128k: audible artifact at 21-22 seconds (2nd "Kyrie") mp3 150k: audible mp3 160k: transparent ogg q0 (47.8k): strong distortion in stereo image ogg q1 (62.8k): stereo image; colored sound ogg q2 (79.2k): stereo image, colored sound, hissing (mainly in beginning) ogg q3 (101.8k): audible hissing ogg q4 (116.4k): transparent
J.S. Bach, Das wohltemperierte klavier: prelude nr. 14 Leon Berben, Harpsichord Brilliant Classics 99362 Comment: A budget edition; I'm not really a fan of harpsichord music, but since harpsichord is reputedly hard to compress, I thought I'd give it a try. mp3 96k: dull (missing high frequencies) mp3 112k: dull mp3 128k: somewhat dull mp3 150k: transparent ogg q0 (65.4k): stereo image, dull sound ogg q1 (79.2k): stereo image, a bit colored ogg q2 (96.5k): fuzzy, hissing middle register ogg q3 (131.6k): nearly transparent ogg q4 (162.0k): transparent
Hugo Wolf, Goethe Lieder: Mignon Geraldine McGreevy (soprano), Graham Johnson (piano) Hyperion CDA67130 mp3 96k: small artifacts on consonants ("ein *S*anfter wind") mp3 112k: very small artifacts mp3 128k: transparent ogg q0 (38.1k): ringing and hissing in piano intro ogg q1 (51.9k): ringing in piano ogg q2 (74.7k): some hissing in piano ogg q3 (96.2k): nearly inaudible coloring ogg q4 (109.1k): transparent
Roberto Roena, Mi Mambo Nascente NSCD 039 "Salsa Moderna" Lots of percussion and trumpet mp3 96k: dull mp3 112k: somewhat dull mp3 128k: somewhat dull percussion mp3 150k: transparent ogg q-1 (53.2k): dull/distorted percussion (cymbals) ogg q0 (68.0k): transparent ogg q1 (82.0k): ogg q2 (95.5k): ogg q3 (118.8k): ogg q4 (137.2k):
mp3 --abr 128and
ogg -q3IIRC. The recordings are quite noisy due to constraints on where I could put the microphones. At first I couldn't hear much difference with the originals (i.e., a 290 kbps ATRAC-encoded minidisc recording, see below), but later I discovered to my surprise that Ogg Vorbis still had audible distortions while mp3 was transparent to me, even with identical bitrates. (The ogg files on the above website are a bit smaller, about 105 kbps)
The ogg distortions are in this case a kind of "rough" sound. I didn't invent that term, but it fits quite well. It is a kind of noise, but not a white noise like tape hiss but rather a feeling that someone is making electrical discharges on the background.
Reportedly, 290 kbps ATRAC is nearly transparent. My experiences are different, something I noticed when I was working with amateur choir recordings. I suspect that I gave the ATRAC encoder a hard time because I made the recordings at a rather low level with a lot of white noise on the background. The result is an artifact that sounds like a car with a owner that is desperately trying to start the engine. You can hear this artifiact both on the MP3- and Ogg Vorbis-recoded recordings on the Ostrochorus choir website (take the recordings taken in 2003 and 2004).
(When you make a live recording, you have to take a safety margin to prevent clipping loud passages and you can't adjust the recording level when you are singing in the choir. So it's -10 dB most of the time. Also, with just a single stereo microphone pair you can't put them too close or the people who happen to be close to the microphone will dominate the recording)