Hey everyone,

Since there are quite a few audio experts on these forums, I figured I would ask a question that has been bugging me for a while now. I am thinking of getting an ipod sometime in the future, when I can afford one. Now, in order to fit as many songs on it as possible, obviously file sizes of the songs are an issue. When encoding in AAC format, I was wondering if anyone happens to know if there is a significant difference in sound quality between songs encoded in 128 kbps and 160 kbps. It's difficult for me to say, because I feel like me ears are really untrained to tell a difference, but I know many of you have run tests about this sort of thing (which I have no idea how to do). Sometimes, in the the past I have enjoyed encoding in 192 kbps, but that sort of rate tends to generate rather large file sizes. So... in other words, should I just stick with 128 kbps or increase the files sizes slightly and go for 160 kbps, assuming that there is a big difference in sound quality, if there actually is? Thanks in advance for any input.

--Jeff

Only your ears can tell you. When you get your iPod, try loading some samples of 128kbps and 160kbps music on it and see if you can hear the difference. If you want to start encoding now, try to ABX 160 and 128 on whatever system you have now. If you can't ABX the files in a home environment, you probably won't be able to in a portable environment, either.

Personally, I go with 128kbps for portable use. Generally, the portable environment introduces so much noise that encoding at higher bitrates is not a good trade off between quality and files size. Of course, YMMV.

Forgive my ignorance, but what exactly is ABX?

negritot

I had the same dilemma a year ago when I started my PC audio collection, & I was misslead by the same kind of post TempestGarden answered (see nothing bad),
so I started ripping in 128kbps & after several months when I finally understund how bitrate increase ... I deleted all & re-ripped in 160kbps ...

So I'll do my best to make you avoid this misstake:
Instead of trying to find a perfect bitrate (which is a myth) you would better ask yourself:

1: What is the minimum bitrate under which you would delete a rip ? (Crap Rips)
2: What is the maximum bitrate above which you woud delete a rip ? (Overkill Rips)

Here was my personnal answer 1 year ago:

1: 128kbps is (was) my min (it's not anymore now)
2: 256kbps is my max (as its 128kbps X2)
(& correct me if I am wrong but you seem to be not far from that very commun way of thinking)

At first look it seems logical so I started ripping at 128kbps ...

But this is forgetting how Audio Bitrates increases:

Range 1 - 0040-0048-0056-0064Kbps (+008Kbps Step) LQ-Streaming
Range 2 - 0080-0096-0112-0128Kbps (+016Kbps Step) MQ-Portable
Range 3 - 0160-0192-0224-0256Kbps (+032Kbps Step) HQ-Backup

ripping at 128kbps while you think the best audio range is range 3: 160-256kbps,
is a paradox ... if you push the logic further then 128kbps becomes obsolete for you because 128kbps is NOT a high quality bitrate ... & is NOT in the +32Kbps Step Range

now it depends on your use:
you said you used to rip at 192kbps, so you are a "range 3" ripper, you can save space by ripping at 160kbps it's safe as you don't switch of bitrate range.

but going 128kbps is a major choice as you un-noticably switch to one range lower...

95% people don't even know & notice that this is a major switch (even HA operators ... as some of my posts (maybe this one too ) get erased when I tryed to explain that fact)

but now I am not a stupid "anti" range 2: 80-128kbps ... what you need to understand is that each range as its optimized use ...
Range 3 is for transparent High Quality PC Backup
while Range 2 is for Medium Quality Portable (or Video)

I can't tell you which is better from 128kbps or 160kbps, it's weither you want Medium Quality or High Quality ...
1: if you can re-rip later & will only listen to the file on an Ipod, then go 128kbps
2: if you can't re-rip later & will listen both on PC & Ipod, then go 160kbps

The most important thing is that you know there is a hole between the target use of range 2 & the target use of range 3.

The "audio experts" help you are requiring will only (at best) tell you that transparency is most of the time reached somewhere between 160 & 192kbps
& that you have to "trust your hears" ... by a wonderfull luck both their listening tests & my strange bitrate ranges theory agree on 160kbps as minimum
... so ... that's all folks...

Hope it Helped, HR

for the full "strange bitrate theory" see also:
http://www.hydrogenaudio.org/forums/index....topic=27706&hl=

ABX is when you take two pieces of audio and try to tell them apart. The classic example is an audio switcher box or piece of software presenting three options, A, B and X, with X being randomly assigned to A or B. If you can consistently tell whether X has been assigned to A or B, then the two samples can be considered different for your ears.

As for bitrate, personally, for portable use, quality doesn't matter, only being able to cram as much music on there as possible. If I'm mowing the lawn, even with good isolating earbuds, I doubt I could ABX 32 kbps with the original. =D

I did some listening tests of my own a while back when deciding on an AAC bitrate and I decided on 128kbps because any difference between the 128kbps AAC and original file were not really noticeable to me during casual listening and the minor improvements of using 160kbps was not worth the extra file size in my opinion. Though in my ABX tests my transparency level was 224 kbps on the samples I tested. 192 kbps was real close to transparency and if I were to encode at a high bit rate it'd be at 192. But as said, it all depends on your ears. Do some listening tests of your own and come to your own conclusion on which is best. Though, I and others on this board will probably love giving you our opinions.

As always it's best for you to decide, but a couple other variables are important here. What environment are you going to be listening (busy city streets, quite library, etc.) and what headphones are you going to be using (stock or something better).

Personally, I think up to the 192 and 224 kbps comparison show differences in the best case scenarios (quiet with revealing headphones and amp) and are worth the extra space. After that it stops for me.

Using Radiohead's HTTT, as an example, the resulting album size difference between 128 and 160 kbps is 12.9 megs. Do your listening test under your conditions and then decide if it's worth that.

The "sweet spot" for me is 160Kbps. The music still sounds good without taking up too much space on the iPod.

I tend to agree on that for most music. Some type of music (e.g. piano, hardrock) seems to benefit significantly from higher encoding speeds.

Some of my observations concerning encoding and the iPod can be found on
http://members.brabant.chello.nl/~m.heijligers/ipod/

Recently, I've added a LAME MP3 comparison.

Marc

Bear in mind that the higher the bit rate the quicker you'll deplete your iPods battery's charge. Personally I use 128kbps AAC and for portable use this is ideal for me. Also bear in mind that at 160kbps MP3 the battery life is the same as 128kbps AAC so you may wish to consider LAME 160kbps ABR versus 128kbps AAC. I use AAC because LAME isn't integrated into windows iTunes, if I could use LAME from iTunes I may have taken a different route.

For mobile listening 192kbps AAC is really overkill IMHO however only your own ears can tell you if you can detect a difference through your portable headphones on a train/bus/plane.

As an aside I have been trying out music stores and Napsters 128kbps WMA sounds poor compared to iTunes 128kbps AAC. The AAC is very difficult to differentiate from the the original CDDA, the WMA sounds awful, swooshing noises and other artefacts.

This method works well for me if I want to fit as much music as possible:

1) encode at 128k or similar

2) listen casualy in a quite room.

3) If quality is more or less ok run a little abx test. Don't try hard, just look for big fat ugly artifacts that you can abx 16/16.. Can't find them ? try to abx different music.. Still can't find them - GOOD! , stick with this encoder setting and save space. So maybe you did abx something. Ask yourself " how bad is it ?" . If its trivial or not very annoying then it is a non-issue with portable or casual use.

I started with lame APS for portable use then APS -Y, APM (-V4) and now I am getting good results using V6 (120k). Even V7 can be very acceptable for portables.

Can you explain more about the quicker depletion? What causes this faster depletion?

Marc

Basically, the higher the bit rate the more the iPod needs to access its hard disk. The more hard disk reads, the lower the battery life.

But the higher decoding complexity, the higher power consumption.
That is why on an IPod, a 160kbps mp3 is leading to the same battery life as a 128kbps aac. (at least according to Apple)

I never seen that. Do you have any links? (To Apple that is...)

For the record, Apple recommends keeping most tracks under 9MB for optimal battery life. What this means exactly is anyones guess, though obviously it relates to at least HD spins and buffer use. So assuming average size pop, etc. songs of 4-5 minutes in length you should be able to encode up to 224 kbps.

i've wondered about this for a while... there's a definite trade-off between quality and filesize, but when we're talking iPods et al, we're talking 4 gigs or higher.

i'm struggling to think of a time when somebody would listen to 4 gigs worth of ~160Kbps music in one session. i certainly couldn't stand it anywhere near that long.

with that in mind, filesize becomes much, much less of an issue (at least to me).

i can go on a 2 month holiday with 2 CDs worth of --aps mp3. 4 gigs means you don't have to sacrifice quality at all, i think. after all, "portable" doesn't necessarily mean "noisy environment" - there's plenty of quiet places when you're on the move (and i use nice big cans even with my crappy mp3 CD player because i've become used to the nice sound, and the earbuds keep falling out...).

this is probably a little OT, but it's something that i would consider when deciding on bitrates for portable use.

too bad iTunes doesn't do VBR... i have no idea why apple haven't implemented it, considering AAC is meant to be VBR.

Well, it isn't CBR either...

No one uses it like that. The idea is that you don't have to guess in advance what you may want to hear later on. The more music you can fit on the portable, the more likely it is you'll always have something that you'll feel like listening to.

That is not exactly true that VBR must be better in quality than Constant Bitrate..
I did some serious studies of the FHG MPEG AAC evaluation program and also iTunes..

It seemed to me that actual bits requirement is rather constant for most frames even at 96 kbps.. especially when there is a switch between block size..
So, VBR doesn't really improve quality very much..

A poorly implemented encoder would have bits consumption varying greatly from frame to frame especially during block switching and thus VBR will help a lot in improving quality..

wkwai

You must remember that the iTunes AAC encoder comes from QuickTime. And QuickTime's main purpose is streaming.

When you do streaming over limited bandwidth channels, VBR is a bad thing, since bitrate peaks will lead to stutters.

It seems Apple already implemented (true) VBR coding in iTunes, as it was available in the QuickTime 6.6 demo in the WWDC CD.

Are you talking about AAC only, or lossy encoders in general (including MP3 and Vorbis)?