1 post tagged “audio compression”

The world is full of mp3 players and many people own and carry them around next to their mobile phone. You can find anything from 1 GB microsized music dice to slimwaisted 160GB iPod-classic's. When only parts of my music collection fits on my phone I find I wanted to play that one number that is missing... But do I really need to lug an 160GB iPod with me for just music? Skip to the How-to to get a quick solution or read the background first for an informed solution.

Mp3 and compression

When mp3-compression became available it was possible to store  high-sound-quality music rather memory efficient (read: affordable) onto your PC for random access and playback. Struggling with bitrates and noisy soundcards it was still largely about: 'because I could'. With increasing cheaper diskspace, better soundcards and compression techniques like AAC, mp3Pro and WMA9 it became more useful and practical. It became practical for me when convergence hit the mobile phone. My trusty SonyEricsson w800i could not only take 2.1MPixels pictures, it could play music. As such it had a cool orange color and sported the Walkman logo...

So several years ago I made the effort of converting all my CD's into 320 kbps mp3 and stored them on my PC. At that time 320 kbps was needed to preserve the quality. Admittedly mp3-codecs were then sufficiently efficient good that 192 kbps might suffice. But in order to recode them later to lower bitrates without irritating recoding errors the bitrate of 320 kbps was a much better choice.

Recent developments into compression formats like AAC, HE-AAC, mpc and Ogg show that at 128 kpbs a perfect sound quality can be achieved. A quality where all sound artifacts are beyond the threshold of human perception. See soundexpert.info's 128 kbps testresults. AAC is doing very well, and it's successor HE-AAC v1 is doing even even better in those results. 64 kbps HE-AAC v1 (aka eAAC) performs close to perfect which is incidently only slightly better than HE-AAC v2 at a lowly 48 kbps, aka eAAC+. Compression formats which the Nokia N95 and many of the NSeries phones support.

Simply explained AAC +SideBandReplication = HE-AAC v1. AAC + SBR + Parametric Stereo = HE-AAC v2 = eAAC+. SBR (sideband replication) is mostly useful upto 128 kbps and PS (parametric stereo) up to 48 kbps. More about it can be found on the Coding Technologies HE-AAC page. In short, above 48 kbps eAAC+ defaults to eAAC encoding and above 128 kbps eAAC+ defaults to AAC encoding.

Accidently, 48 kbps eAAC+ is the default encoding quality of the Nokia Music Manager. This quality is considered by the progam to be good quality and optimal for mobile application. An additonal bonus of the 48 kbps HE-AAC with SBR and PS encoding is that is designed to be very power efficient to decode/play. Better than mp3 or regular AAC. 64 kbps eAAC is considered by the Nokia Music Manager to be excellent quality.

Howto

My collection of mostly 320 kbps encoded mp3's (some are 192 kbps) on my home PC requires about 26 GB of diskspace. Converting it into eAAC+ at 48 kbps reduces it into 4.65 gigabyte. Not bad for 'good' not excellent rated compression. We are talking here about 9 days of contineous music. Add about a 1.5GB for the Maps of USA or either the Europe for Nokia Maps and you have about 1.5 GB left for recording film, photos on a 8GB memory card. Do you want excellent quality nearly indistinguishable from the original? Go 64 kbps if you are a classical music loving audiophile. But otherwise it is not worth it, especially not on your phone.

How to convert? Although Nokia Music Manager can do the encoding for you it does not cope well with encoding my 3000+ music files. It simple crashes at some point. The free version of WinAmp however works great and gives a very nice quality. Nero gives even better encoding results. Simple import your mp3's into the winamp music libary and 'send to' the 'Format Converter'. Select an output folder and the first AAC Plus converter in the list. Next set 48 kbps and parametric stereo. After 24 hours or so it is finnished converting everything on a 2.4 GHz Pentium 4.

Audio quality, practical aspects and it's pricetag

An 8 GB microSD card costs about 50 euros and can store about 11 days of music at nearly indistinguishable CD quality in 64 kbps eAAC or 15 days of music if you are happy with a pretty good mobile quality of 48 kbps in eAAC+. In comparison a separate iPod or iTouch with regular AAC at 128 kbps would in comparison require at least 21 GB of diskspace. Neither iPod or iTouch come close into the 50 euros price range. In fact iPod classic prices currently start around 230 euros. Of course a 80 Gigabytes mp3-player is very cheap for that price. But it is way to much for just music.

A good argument might be the sound quality. My N95 has a slight hiss at low volumes, the iPod has a better sound. Well this is true. However a good bluetooth stereo headset can be bought for a mere 50-60 euros. The bluetooth headset has it's own D/A converter and a good one has no background hiss. The additional advantage is that if you buy a bluetooth headset like the Nokia BH-500 with a regular 3.5 mm headphone connector, you can connect any headset you like. You can even connect it to your stereo allowing it to work as a A2DP gateway. Playing music straight from the couch over the stereo. At this point you would still have paid only 110 euros versus a 230 euros for the cheapest iPod classic which has no bluetooth support or a remote controlled headset. Seems to me there is even plenty enough money left to shell out for a spare phone battery of 20 euros ;-)

Currently neither the iPod, the iTouch or the iPhone support any of the better HE-AAC codecs, silly is it not? Particular since Apple put AAC on the consumers map. This year 16GB and 32GB microSD cards are entering the market giving eAAC+ capable phones an even stronger position particular against the iTouch/iPhone in musical terms. Even audiophiles with very large music collections (800+ albums) can carry all their music in their 'pocket' at 128 kbps in top notch HE-AAC. No battery draining streaming, no network load or cost, no ORB or winamp remote required. Just random music access from you on your phone, a properly spelled phone. You see it, don't ya? There is no i in these phones!

P.S. At 3000+ songs the music player starts becomes a bit sluggish when browsing the songlistings. Minor acceptable delays occur when opening the song/artist/album lists.

Update: A comparison of eAAC+ (48 kbps, SBR+PS) and AAC+ (64 kbps, SBR) can been found at the Hydrogen Audio Forums. Particular this result gives a good representation of the practicality of using parametric stereo. It seems a HE-AAC V3 standard with a variable stereo bitrates would be useful to be developped for classical music.