Mastered For iTunes

1. When you buy a CD/download and you discover it's limited/clipped: take it back and get your money back.
   
2. Buy older CDs 2nd hand as in general they have been mastered better.
   
3. Avoid anything with 'remastered' on it like the plague.
   
4. Sign up to Apple and try 'Mastered for iTunes' tracks.
   
5. Run them through a declipper: i.e. use SeeDeClip4.
   

Mastered For iTunes is a high quality music mastering/selection process invented by Apple. They specifically mention gatekeeping points that may cause tracks to be rejected, highlighted below in blue. This is a very good way to get better mastered music. In general we recommend the followig strategies:

Part of the quality of Mastered For iTunes is due to Apple's insistence on masters meeting a particular quality. The record industry keeps creating dud CD audio tracks that we must assume that it got such a problem that Apple decided on an entirely new brand with a quality gatekeeping role and a serious of guidlines on what they were looking for.

The main spec may be found here: Apple.com = mastered_for_itunes.pdf.

A major part of the spec is devoted to detecting, measuring and avoiding clipping. This is a major step forward for digital audio.
It mentions clipping/clipped 46 times and contains the following statements about clipping:

• Improved Conversion and Encoding for AAC
  
  
  • Clipping is a form of audio distortion and can be caused in many ways. In general, it is the result of the amplitude of a signal becoming too great to be accurately represented by a system.
    In an amplifier this can occur if one attempts too much amplification—the top of the signal is cut off, or “clipped.”
    In digital audio this can occur when a signal falls outside of an allowed bitdepth range.
    
  
  
  
• Because this SRC outputs a 32-bit floating-point file, it can preserve values that might otherwise fall outside of the permitted amplitude range. This critical intermediary step prevents any aliasing or clipping that could otherwise occur in SRC. It is this 32-bit floating file that’s used as the input to the encoder and is one key reason for such stunning results.
  
  
• Be Aware of Dynamic Range and Clipping
  :
  Many artists and producers feel that louder is better. The trend for louder music has resulted in both ardent fans of high volumes and backlash from audiophiles, a controversy known as “the loudness wars.” This is solely an issue with music. Movies, for example, have very detailed standards for the final mastering volume of a film’s soundtrack. The music world doesn’t have any such standard, and in recent years the de
  facto process has been to make masters as loud as possible.
  :
  With digital files, there’s a limit to how loud you can make a track: 0dBFS. Trying to increase a track’s overall loudness beyond this point results in distortion caused by clipping and a loss in dynamic range. The quietest parts of a song increase in volume, yet the louder parts don’t gain loudness due to the upper limits of the digital format.
  
  Although iTunes doesn’t reject files for a specific number of clips, tracks which have audible clipping will not be badged or marketed as Mastered for iTunes.
  :
  If the original digital audio data is at 0dBFS, oversampling can result in undesirable clipping. And if the original was already clipped, oversampling can make it worse. A growing consensus is emerging that digital masters should have a small amount of headroom (roughly 1dB) in order to avoid such clipping.
  :
  Whatever you decide—exquisitely overdriven and loud, or exquisitely nuanced and tasteful—we will be sure to encode it and reproduce it accurately. We only ask that you avoid clipping the signal.
  
  
• Master for Sound Check and Other Volume Controlling Technology
  The effect of Sound Check, as well as other volume-controlling technologies, is that songs that have been mastered to be too loud will be played back at a lower volume, letting listeners more easily notice any artifacts or unintentional distortion.
  Because many such technologies are available to listeners, you should always mix and master your tracks in a way that captures your intended sound regardless of playback volume.
  
  
• Remastering for iTunes
  When remastering for iTunes, procedures and best practices similar to mastering for new releases should be followed. You should always work from the best available master, carefully monitor gain to avoid clipping, and audition the encoding process and finished files on an iOS device.
  
  Although it’s possible to remaster from a previously mastered CD source with positive results, in order to qualify as Mastered for iTunes remastered content must begin with a high resolution digitization of the original analog source and must sound noticeably superior to the previously released version.
  
  Songs and albums submitted to the iTunes Store as remastered content will be reviewed to ensure that the sound quality shows discernible improvement.
  
  
• Mastering Tools
  
  
  • afclip. The afclip command-line utility can be used to check any audio file for clipping
    
  • AURoundTripAAC Audio Unit. The AURoundTripAAC Audio Unit can be used to
    compare an iTunes Plus file to the original source audio file to check for clipping
    
  
  :
  The following sections include instructions for using some of these tools to convert audio to iTunes Plus AAC and checking audio for clipping
  :
  
  ....etc...
  

So you can see if you want to avoid the clipped masters endemic in the CD world then Mastered For iTunes ia s very good place to look.