iTunes encoding quality

[beef]

Joint stereo sometimes introduce artifacts... If you aren't concerned about the space, I'd encode at 256kbps, stereo. I wouldn't bother using VBR. It doesn't really save that much space.

you can use lame to encode mp3 with iTunes.

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edited (addtion)

forgot when, but 300 'audiophiles' tested the quality of mp3 with original cd, 128kbps mp3, and 256kbps mp3. They picked out 128kbps mp3's 90% of the time...while most times 256kbps passed. They used quality audio equipment at studio, so it's not Fisher's bullshit boombox. and mp3's were decoded on Macs (encoded on PC though)

so if you're after quality, I wouldn't go with 128kbps.

If you are using lame, you can use JS. It's better than others. If there's too much separation, it'll just use stereo for that frame.. I dunno what encoder iTune uses.

[Essage]

...a song encoded in 192kbps takes up 1,5 times of what a 128kbps does.

But I'd say it's really worth it.

I´s easy to calculate the size of an mp3. kbps stands for "kilo bit per second". 128kbps takes up 0,96MB/min, (128*60)/8=960
192kbps takes up 1,44MB/min, (192*60)/8=1440
320kbps takes up 2,4MB/min, (320*60)/8=2400

128kbps sounds really bad. 160 is ok, but not good, can still hear some distorsion. While I think 192 is really good. It´s the best compromise between size & sound. So I rip all my CD´s in 192. But if there´s a really good song that I know I will listen to the rest of my life (almost), I rip it in 256.

I have a Sony STR-DB940 DD/DTS Reciever (about 650$, awardwinning), a Sony ...-XB930 CD Player(400$), and Audio Pro Black Diamond speakers (500$/pair, very priceworthy).

[GadgetLover]

OK, so new sub-poll:

For those of you audiophiles that prefer higher quality encoding, which do you prefer (again, keeping in mind quality vs. size sacrifice)?

a) 192kbps, stereo (96kbps per channel);
b) 256kbps, stereo (128kbps per channel);
c) either 192 or 256 (above) but in JOINT STEREO;
d) 320kbps, stereo
e) 256 or 320 but with mono set to 8kbps (as Chem Geek suggests -- I've never tried it).

In other words, has anybody else done the mono reduction thing?

And what about the custom settings in iTunes -- if you encode at higher than 192kbps, you must use them, so what should the "smart encoding" and "filter frequences below 10hz" "channel (auto, stereo, etc)" be set at??

[Myke]

As a Hi-Fi obsessive who has now become a Mac obsessive too, I say forget MP3, if you want quality.

ANY kind of compression will be audible with even a half decent hi-fi.

So, what we are talking about is compromise - and you trade off quality for size.

Anything above 160 is going to give you sufficient quality not to wince, but you'll still flatten the sound and the high frequencies will lack energy.

At best, your MP3's will sound like they are playing on a mini-disc, which use a similar kind of compression.

Some high end hifi can make the music sound sweet, just the same (valves usually) - but on more analytical gear you can hear graininess, akin to pixellation on JPEG photo files.

Did someone mention B&O catridges by the way? Wish we could stll get the good ones in the UK, they only sell the low end version here! The top of the line MMC was my favourite of all time.



Rogers e40 valve amp
Quad ESL 63 speakers
Audionote CD player
Dunlop Systemdeck turntale with Ortofon line contact stylus.

Oh ...and a G4 733

[beef]

I agree to some extent...

I'm not an audiophile, and my stuffs (I wouldn't bother listing, unless requested) will prolly be considered mid-fi by real audiophiles...

so, can I hear the difference between CD and mp3?

actually yes, even at 256kbps... but in my opinion, that has more to do with the soundcard of my mac, the output (headphone out...) and the cable connecting mac and my preamp.

so if I'm listening to music, while doing nothing else (or little), I'd always use CD. But if I'm listening to music as some background music while I do other stuffs, I can live with iTunes. The advantage being I can just use a playlist, and don't have to change CD, etc...I can just keep working.

If I play CD or mp3 on my mac, they'd both sound shitty because the builtin speaker ain't worth a damn...

If you determine the quality of mp3 by how much difference from CD you can actually detect, then the equipment you use will have as much to do with the numbers, etc......

but...mp3 encoders are improving.. and ATRAC3 has come a long way, too... I remember the first time I heard MD... it was just shitty. My feeling was "smaller than tape, no-where near CD". I dunno when was the last time you used MD, but it's alot better than that now. I wouldn't mind using it now...as portable media.

in any case... I've always felt it's your ears that must be satisfied... and as I've said, your equipment will affect how you come to your decision. I "recommended" 256kbps stereo (ms if you're using lame), but the real solution probably is just to play around with a few of your favorite tracks...if you can hear the difference, then calculate the change in file size (total) and see if it's worth it... if you can't hear the difference, then why bother.

anyone know what encoder iTunes comes with, btw? I'd definitely encourage you to get lame encoder.

hmm.......I've always imagined it'll be easier to get that kinda stuffs in UK... after all, alot of people go there to hunt for old records... Quad 63...how long have you had that thing? have you listened to the new quads? nobody around here has one...

[rezba]

Does your 128kbs mp3 let you happy earing them ?
Sound is so related to your earing skill ! I have pretty good earing, compensing my deficient eyes. I noticed that 192 give me back a quite full sound with a 3 or 5 pieces sound system. But most of my friends don't ear the difference between a 128 and a 192.
I encode in 192 to preserve a good quality when a encode my mp3s in AIFF to play them on my hifi. When it's symphonic music, I try to catch 256 mp3. It's better. But it take to much place to do it systematicly.

However, does anyone ever eared the sound of a ATP 700 sound system. For a quarter price to the Harman Kardon, it's so.... waouh !

[GadgetLover]

FYI (Fraunhofer is the inventor of mp3 technology along with Thomson RCA)

http://www.iis.fhg.de/amm/techinf/layer3/index.html

===
MPEG Audio Layer-3
History Quality Details

History**

In 1987, the Fraunhofer IIS-A started to work on perceptual audio coding in the framework of the EUREKA project EU147, Digital Audio Broadcasting (DAB). In a joint cooperation with the University of Erlangen (Prof. Dieter Seitzer), the Fraunhofer IIS-A finally devised a very powerful algorithm that is standardized as ISO-MPEG Audio Layer-3 (IS 11172-3 and IS 13818-3).
*
Without data reduction, digital audio signals typically consist of 16 bit samples recorded at a sampling rate more than twice the actual audio bandwidth (e.g. 44.1 kHz for Compact Disks). So you end up with more than 1.400 Mbit to represent just one second of stereo music in CD quality. By using MPEG audio coding, you may shrink down the original sound data from a CD by a factor of 12, without losing sound quality. Factors of 24 and even more still maintain a sound quality that is significantly better than what you get by just reducing the sampling rate and the resolution of your samples. Basically, this is realized by perceptual coding techniques addressing the perception of sound waves by the human ear.
*
Using MPEG audio, one may achieve a typical data reduction of
*
1:4 by Layer 1 (corresponds with 384 kbps for a stereo signal),
1:6...1:8 by Layer 2 (corresponds with 256..192 kbps for a stereo signal),
1:10...1:12 by Layer 3 (corresponds with 128..112 kbps for a stereo signal),
still maintaining the original CD sound quality.
*
By exploiting stereo effects and by limiting the audio bandwidth, the coding schemes may achieve an acceptable sound quality at even lower bitrates. MPEG Layer-3 is the most powerful member of the MPEG audio coding family. For a given sound quality level, it requires the lowest bitrate - or for a given bitrate, it achieves the highest sound quality.
*

Sound Quality**

Some typical performance data of MPEG Layer-3 are:
*
sound quality bandwidth mode bitrate reduction ratio
telephone sound 2.5 kHz mono 8 kbps * 96:1
better than short-wave 4.5 kHz mono 16 kbps 48:1
better than AM radio 7.5 kHz mono 32 kbps 24:1
similar to FM radio 11 kHz stereo 56...64 kbps 26...24:1
near-CD 15 kHz stereo 96 kbps 16:1
CD >15 kHz stereo 112..128kbps 14..12:1
*) Fraunhofer uses a non-ISO extension of MPEG Layer-3 for enhanced performance ("MPEG 2.5")
*

In all international listening tests, MPEG Layer-3 impressively proved its superior performance, maintaining the original sound quality at a data reduction of 1:12 (around 64 kbit/s per audio channel). If applications may tolerate a limited bandwidth of around 10 kHz, a reasonable sound quality for stereo signals can be achieved even at a reduction of 1:24.
*
For the use of low bit-rate audio coding schemes in broadcast applications at bitrates of 60 kbit/s per audio channel, the ITU-R recommends MPEG Layer-3. (ITU-R doc. BS.1115)
*

Details**

Filter bank
*
The filter bank used in MPEG Layer-3 is a hybrid filter bank which consists of a polyphase filter bank and a Modified Discrete Cosine Transform (MDCT). This hybrid form was chosen for reasons of compatibility to its predecessors, Layer-1 and Layer-2.
*
Perceptual Model
*
The perceptual model is mainly determining the quality of a given encoder implementation. It uses either a separate filter bank or combines the calculation of energy values (for the masking calculations) and the main filter bank. The output of the perceptual model consists of values for the masking threshold or the allowed noise for each coder partition. If the quantization noise can be kept below the masking threshold, then the compression results should be indistinguishable from the original signal.
*
Joint Stereo
*
Joint stereo coding takes advantage of the fact that both channels of a stereo channel pair contain far the same information. These stereophonic irrelevancies and redundancies are exploited to reduce the total bitrate. Joint stereo is used in cases where only low bitrates are available but stereo signals are desired.
*
Quantization and Coding
*
A system of two nested iteration loops is the common solution for quantization and coding in a Layer-3 encoder.
*
Quantization is done via a power-law quantizer. In this way, larger values are automatically coded with less accuracy and some noise shaping is already built into the quantization process.
*
The quantized values are coded by Huffman coding. As a specific method for entropy coding, hufman coding is lossless. Thus is called noiseless coding because no noise is added to the audio signal.
*
The process to find the optimum gain and scalefactors for a given block, bit-rate and output from the perceptual model is usually done by two nested iteration loops in an analysis-by-synthesis way:
*

* Inner iteration loop (rate loop)
*
The Huffman code tables assign shorter code words to (more frequent) smaller quantized values. If the number of bits resulting from the coding operation exceeds the number of bits available to code a given block of data, this can be corrected by adjusting the global gain to result in a larger quantization step size, leading to smaller quantized values. This operation is repeated with different quantization step sizes until the resulting bit demand for Huffman coding is small enough. The loop is called rate loop because it modifies the overall coder rate until it is small enough.

* Outer iteration loop (noise control/distortion loop)
*
To shape the quantization noise according to the masking threshold, scalefactors are applied to each scalefactor band. The systems starts with a default factor of 1.0 for each band. If the quantization noise in a given band is found to exceed the masking threshold (allowed noise) as supplied by the perceptual model, the scalefactor for this band is adjusted to reduce the quantization noise. Since achieving a smaller quantization noise requires a larger number of quantization steps and thus a higher bitrate, the rate adjustment loop has to be repeated every time new scalefactors are used. In other words, the rate loop is nested within the noise control loop. The outer (noise control) loop is executed until the actual noise (computed from the difference of the original spectral values minus the quantized spectral values) is below the masking threshold for every scalefactor band (i.e. critical band).*

[martek]

There will be a difference in sound quality between one bit rate vs another ... and between mp3 and CD. MP3 is a lossy compression in which some of the data is always thrown out in the interest of file size. Researchers are becoming more clever about *which* data can be tossed out while keeping the *perceived* sound quality relatively high.
It's rather irksome that the marketing droids affix the label "CD quaility" to mp3 devices/software when technically, it's not true. CD "quality" is 16 bit, 44.1khz!

I've done some experiments and have found 160k about the lowest bit rate I can stand to listen to music with. Anything lower there's too many compression artifacts. As a rule, if the CD sounds kinda crummy to begin with, I'll encode at 160, if it's a medium quality recording I'll select 192, and if it's a jazz or classical recording of high quality I'll choose 256 or higher. I find these settings sound fine on my G3 with Boston Acoustics sat/sub 3-piece speakers that I use at work.

I also have an audio system at home comparable to some of the previous posters and I can say without a doubt that mp3 encoded audio sounds nothing like the original CD. Depending on the music you can get acceptable results (comparable to the sound of FM radio I'd say) but nothing real great. This may change in the future with more sophisticated compression algorithms that (hopefully) don't throw out any data. If anyone cares (probably not, but I'll say it anyways ) LP records still sound better than CD's.

Bottom line? Go with what your ears tell you and don't worry about it.