Sound Check vs Replay Gain, iTunes Vs. Winamp

Sound Check in iTunes and iPods is about the same as Winamp’s Replay Gain feature.  In this piece, we discuss Sound Check vs Replay Gain.

Sound Check vs Replay Gain Introduction

What is Sound Check?  What is Replay Gain?

The two automatic volume control mechanisms help ensure that the recordings in your audio library play at roughly the same average volume.  This reduces the differences in volumes as one recording ends and the next one begins. Thus, the objective of both Sound Check and Replay Gain is the same.

Each method suffers various pros and cons.  But neither algorithm is perfect. Nonetheless, we find that with either system, we must adjust the volume far less when the next song plays. Both systems raise the volume on very quiet songs. And they lower it on very loud songs. Thus all songs play at about the same loudness.

Sound Check vs Replay Gain: What the Have in Common

Neither Compress an Audio Rcording

Neither Sound Check nor Replay Gain compress the audio. Both actually find what the overall volume setting of the song should be before  it plays.  This differs from dynamic, ongoing volume tweaks done during play as happens in on-the-fly compression. Both systems set the volume level the same way. Just once, unlike compression, which makes constant readjustments.

Neither ‘Ducks’ Sound Peaks

This means that neither iTunes Sound Check nor Winamp Replay Gain readjusts the volume in response to loud or soft peaks in the song, while its playing.  This means that even with either system enabled, you’ll still have very loud as well as very soft parts in the song.

Both can Limit Dynamic Range

Neither of these software-based volume controls is intended to limit the dynamic range of an audio recording per se.  However, some limiting typically results nonetheless, when the system changes the overall music volume.

When volume goes up, this also raises the noise floor (equipment hiss, hum, and digital conversion noises).  This can reduce the dynamic range if the loud peaks in the recording, as a result of this volume raising, are clipped, as happens on purpose in the iPod’s built-in volume limiter.

Further, when the overall volume is lowered, the volume of the entire recording is lowered, including its loudest parts, which again, reduces dynamic range; that range being the difference in DB levels between the loudest and softest parts of the recording. Both Winamp Replay Gain and iTunes Sound Check suffer from this side effect, particularly whe low to medium level sound equipment is used, with its limited dynamic range capabilities.  Raise the volume too much, and you end up making the quiet parts of the song too noisy and distorting the loud peaks too much.  Lower it excessively, and you too-far dwarf the peaks and may in fact mask out the quieter content.

Both Offer More Constant Average Music Volume

But on the up side: The average volume level of all your music, when playing it in Winamp or iTunes, should be more constant than it is with these volume regulating mechanisms disabled,  Loud passages won’t blast you as much when you turn these features on.  Plus, with very quiet recordings, where the loudest parts aren’t in fact very loud, the quiet parts receive a boost, making them more intelligible.  While the audio purist may cringe at the reductions in realism that Replay Gain and Sound Check can have, for the average portable media player listener, these volume regulators really do save the ears.

Players that do Sound Check Generally do Not Do Replay Gain and Vice Versa 

Also, Winamp does not understand iTunes Sound Check currently.  Nor does iTunes understand Winamp Replay Gain.  That is: When you apply Sound Check to your iTunes Library, playing the resulting files in Winamp does not produce a constant average volume level among the recordings.  Nor do files encoded with Winamp Replay Gain, play with Replay Gain in force in iTunes or on iPods.

Finally, while Sound Check and Replay Gain accomplish the same objectives, Sound Check typically works only when you’re playing your audio files either in the iTunes software, or on an iPod or iPhone.  Replay Gain however, works with numerous other players, but not iPods.  So, if iPods are your players of choice, then you’ll have to use Sound Check to gain the advantages of pre-calculated loudness levels among your audio files. But if you use another player, one that does not understand the Apple iTunes Library database, then you’ll have to use Replay Gain.

Some, but not all media players know how to interpret and respond to the Winamp Replay Gain tags.  But so far as I’ve ever seen, only iPods and iPhones can respond to iTunes Sound Check values.  So pick the sort of player you want, and apply the appropriate system to your music library accordingly.

Sound Check vs Replay Gain, The Differences


Replay Gain is available on many player apps, whereas Sound Check is proprietary, and only found on Apple built products.

Sound Check Occurs More Transparently than Replay Gain

The iTunes Sound Check feature works throughout the iTunes library. In fact, when you import new music and you have Sound Check enabled, iTunes figures out at import time what the appropriate volume for the song should be, and then records that value in its database. You can observe these Sound Check calculations happening right after importing a large bunch of songs. Messages appear in the iTunes status window; something about analyzing volume levels or other text to that effect.  However, in order to apply Winamp’s Replay Gain, you must explicitly initiate the volume calculation operation.  This is not done at importation time. So Sound Check in iTunes is more automatic in iTunes than Replay Gain is in Winamp.

Perhaps this is so because the two software media players use different mechanisms for storing the results of the volume calculations for each file.  Winamp writes the Replay Gain volume settings into tags that become part of each audio file. These tags then move along with the file, and any portable or desktop player that understands how to decode them can set its output volume according to the Replay Gain values.

iTunes on the other hand, seems to store the Sound Check volume setting outside of the file, in a separate meta database, and not in the music files themselves.  So unless you’re syncing to an iPod (a player that receives and understands this additional information in this Apple-dictated format), your player will not adjust itself to Sound Check values.  iTunes Sound Check therefore, appears less portable than Winamp Replay Gain.  It’s unfortunate that iPods cannot respond to Replay Gain encoded files.

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References for Sound Check vs Replay Gain

  1. Replay Gain   on Wikipedia
  2. iTunes Sound Check   on Wikipedia

Revision History

  • 2019-02-25: Added key phrase targeting and more subheadings and tags.
  • 2015-11-28: Added appropriate tags.
  • 2014-11-25: Added a References section, and new categories.
  • 2012-08-25: Published originally.