All about Digital music

[iSonics]

A bit of Background

The complexity in music has increased a lot since the 80’s, which saw cd emerging as the music media. The cross player compatibility between various brands of music players was never an issue. A CD made by Sony could be played on a national music player with same fidelity as on the native Sony one. Similarly, a cd brought from best buy would have equal quality as one you brought from the next door music store. But today’s scenario is very much different from that era. With total lack of any standards in music industry, today’s hardcore audiophiles need to get their homework done in basic digital music knowledge to get the best music experience while ripping their CDs to digital music media.

Most of the standards existing in music world have been invented by Fraunhofer Institute, Germany. It all began in 1987, with a research on high quality digital compression. The made a set of principles for compressing music without much loss of information. One of the basic principle involved in compression is that human ear can hear most of the sounds in the music which are above and below the audible frequencies and also those sounds which are masked by the more louder sounds. It is possible to compress the music by removing those inaudible sounds without human ear able to perceive its absence.

Just for example, a base guitar with loud noise can mask a drummer’s sound. So for reducing the size of the audio file, we can remove those inaudible sounds, without much deterioration of sound quality.

The effect is very similar to that of 50’s Hollywood movie sets with a lot of facades constructed to resemble real buildings.

Here we discuss some seven basic facts to know about your digital music, so that you can enjoy, be it on your Rs.8000 iPod or Rs.800,000 home audio distribution system

Music Formats

Fraunhofer institute with their research came up with mp3 standard for music, short for Motion Pictures Expert Group Audio Layer III. The standard became notoriously famous in 1990’s with foothold in college dorm rooms. The quality didn’t matter that time, but now it does.

There has been invention of a lot more advanced and better codecs since MP3. Broadly categorizing there are two types of codecs, lossless (ALAC, FLAC, AIFF, WMA Lossless) and lossy (MP3, AAC, WMA).

The main advantage of lossless codecs is that footprint of the music file is reduced by up to 60% without noticeable loss in CD’s audio quality; however it requires roughly 400-500 MB of storage per CD of audio digitized.

This way seems to be quite economical with the current tried in falling memory prices and in future you can again burn them back to a cd or play them on high-end music solutions with almost little or no loss in quality of music. Where as the lossy codecs, as implied by their name do not preserve the original quality of the CD, but rather very high compression rates of about 10-12 times smaller than the original size are possible. That is with some loss in the detail of music, it is possible to achieve very high compression rates.

This seems to be mantra behind the runway success of MP3 players notably iPod. With a MP3 compression it was now possible to store a 500 CD collection on 30GB iPod. MP3 was most popular lossy codec as almost all the standalone media players were able to decode it.

Microsoft developed WMA and Apple licensed AAC audio format from Fraunhofer, to address the shortcomings in MP3 standard especially at high compression rates. But these standards being proprietary, work on limited number of media players.

Compression rates

When we talk about compression, then not only the codec used, but the compression ratio as well matters. More the compression, lesser the information a file would contain. Information in digital word is represented by bits and bit rate is the information processing rate at which the information is processed.

In layman terms, increased bit rate allows more information hence better quality of music to be stored and replayed, but with a trade off of bloated size of the file. There is a noticeable difference in listening to two files, one encoded at lower bit rate and other encoded at higher bit rate even with both of them using the same compression codec.

Following table illustrates the quality of sound at different bit rates.

8 kbps Telephone speech quality sound.

32 kbps AM radio quality: speech is full, but music sounds hollowed.

96 kbps FM radio quality: stereo sound, but cracks when played through high fidelity music player.

128 kbps Music sold on iTunes (AAC 128) and Rhapsody (WMA 128): sizes less than 5MB, good for downloads, but can’t be played through high end music system.

192 kbps almost equivalent to CD, listener would have hard time differentiating from the real source. Ideal for portable devices and headphones, but base and high range will wash out when played through a high-end audio system.

320 kbps highest bit rate for MP3, AAC and WMA. Though still considered a Lossy format, sound quality is nearly indistinguishable from the original CD, even when played back through a high-end system.

500 kbps Lossless audio, such as FLAC, ALAC, AIFF and WMA.

1411 kbps PCM standard for manufacturing audio CDs.

Popular online music stores like rhapsody and iTunes sell music at 128Kbps encoding, which though would sound nice when heard on standard iPod headphones, but would perform terribly when heard on a high end headphones or music system.

Hardware and software used for ripping

Most of the amateur CD ripping is done through non commercial home based hardware, which isn’t exactly the best way to do the ripping as compared to top of the line and expensive studio grade hardware, which not most of the people can afford. However, by following some basic guidelines, it is possible to optimize the output of home computer used for ripping the cd to almost 60-70% efficiency.

The very first step is to check the type and configuration of CD-rom drive to see if your data would be extracted clean and complete. See the drive and manufacturer and check if it supports audio extraction. Drives that vibrate excessively and increase RPMs of the disc to compensate for maintaining constant linear velocity can cause a lot of seek errors, which translate to choppy sound, gaps, clicks and other disturbances.

Make sure that the cd rom drive you are using is with highest possible data rate and the drivers for the drive are up-to-date.

The computer to be used for ripping purposes should be equipped with powerful CPU as ripping and encoding are processing intensive activities. Try to avoid running programs in parallel when ripping CDs. Even the basic free softwares like Apple’s iTunes and Microsoft’s windows media player can be used for ripping if you are not comfortable with high end softwares. Always make sure that the output format is what you want, as dictated by the decoding capacity of your media player. Do listen to the first few songs which you encode so that you don’t repent on the months wasted for ripping hundred of CDs with quality you don’t require. Once you determine the settings required for perfect ripping, you won’t have to change much of it.

Error correction software

The desktop computers which we use are not made for audio extraction. A common household cd player, reads continues data with its laser following smooth track. Computers on the other hand, read information in blocks.

The blocks of data are then written to random sectors, which add up the latency resulting in gaps and misses. The disjointed sector reading and writing leaves out important information and based on principle of garbage in and garbage out, the unregulated input creates poor quality output.

This is the reason that computers, laptops and low-end cd ripping hardware create a poor quality output even when the CD is brand new or without any physical damage.

The solution to this is to use error correction algorithms which read overlapped blocks of data and check for any inconsistencies and in case there are, then it directs a reread for that block.

The error correction becomes highly essential, when the CDs being used are old and scratched as they are bound to contain a lot of errors.

There are a few freewares for error correction like CD Paranoia, which provide quite a decent error correction. But many of the people even while using standard programs like windows media player and iTunes forget to realize that these programs are also built with rudimentary error correction techniques, which by default are disabled and can be enabled by going to EDIT > PREFERENCES > ADVANCED > IMPORTING and there selecting “error correction while importing CDs”.

However, you should remember that error correction techniques are both time and processor intensive and it takes almost three to four times the longer the time with error correction being turned on to rip a cd.

But the results are quite better especially when you are doing a very old collection of CDs.