Sound Check Feature

Turning it on is enough to have it scan and equalize all the songs in your library. There's nothing more you need do.

But I've noticed that, even after this, not all the songs are played at equal volume.

Nothing is perfect. You cannot actually "equalize" volume of two greatly different types of music. For example, a hard rock type of song is always going to be louder than somebody playing a flute. 😉

Sound Check will get them reasonably close though.

simply sample the average volume of each song

This is more complex than you make it sound, because "volume" is not a function of the song itself. Human perception plays a big part in what the "volume" level is.

It doesn't seem to be difficult to do

No, it's actually incredibly difficult and quite time consuming because of the above.

Furthermore, a lot of songs start off quiet, and then get louder. What's the "average" volume of those? If the first half is at volume 1, and the last half is at volume 7, then the average is volume 4, and if you're equalizing the volume to be the same as a song of average volume 6, then that means you bump the volume up on it, bringing that 7 to an 8 or 9, which is way too loud... See what I mean? There's a lot of trickiness involved here.

In my case, the Sound Check feature does not get them "reasonably close".

Actually, it probably gets it more reasonably close than you think it does, given the complexity of the process. Like I said, it's not perfect, but it's better than leaving it off.

Also, how does one do this on the iPod?

In the iPod's Settings menu, turn on Sound Check.

The sound check in iTunes doesn't work for me.

I burned two mixed audio CDs from the same playlist (some songs ripped from CDs, some recorded from lp, some "freebie songs" downloaded from websites). The first CD, burned in iTunes with "sound check" enabled, played with very noticeable volume changes...some of the songs I could barely hear, and others would blast. There was no relationship to the type of music, but rather to the source. The second, burned with Nero and "normalize" enabled, was very consistent...some songs sounded a bit louder, but they were the "noisy" ones, musically, so this was to be expected.

I remember sound check seemed to work better in previous versions of iTunes. When it was first put in as a burn oprion I remember being very happy with the results, but in the current version it doesn't appear to do anything.

I remember sound check seemed to work better in
previous versions of iTunes. When it was first put
in as a burn oprion I remember being very happy with
the results, but in the current version it doesn't
appear to do anything.

Don't know about the burn functionality, as I don't burn Audio CD's. Don't see the point. However, Sound Check works great for me in both iTunes and on the iPod.

I remember sound check seemed to work better in
previous versions of iTunes. When it was first

put

in as a burn oprion I remember being very happy

with

the results, but in the current version it doesn't
appear to do anything.

Don't know about the burn functionality, as I don't
burn Audio CD's. Don't see the point. However, Sound
Check works great for me in both iTunes and on the
iPod.

Well, I was talking about the burn option because it's my way of testing it against another software that does volume equalization...don't get me wrong, I really like iTunes but sound check just doesn't work all that well, based on how it compared to the 'normalize' function in Nero. 🙂

Well, I was talking about the burn option because
it's my way of testing it against another software
that does volume equalization...don't get me wrong, I
really like iTunes but sound check just doesn't work
all that well, based on how it compared to the
'normalize' function in Nero. 🙂

Okay, Nero has two methods of "normalization", and it really depends on which you're using.

If you use the Peak Normalization, then the results will probably be worse than Sound Check's, because all your CD's will sound significantly quieter than you expect them to. Peak Normalization is also called "Maximum" mode or "Wave Corrector" in different Nero versions.

If you use the Nero RMS mode, then yes, that will probably sound far better than Sound Check does, to the untrained ear. However, RMS normalization often causes clipping in the final audio CD. And once you learn to notice clipping, it will forever annoy the heck out of you. Ignorance is bliss, I suppose.

Volume levelling is a maze of compromise solutions. Sound Check's method (the same method as ReplayGain uses, although not as robust) is widely considered to be the best all around method to use. It can cause clipping, but seems to be geared to do so only in minor amounts with the Sound Check system.

Oh, I know about clipping, but the disparities in volume, from one song to the next (and running to the player to turn it down because it's suddenly rattling the walls) is far more annoying. Besides, these are lossy songs being played, and some of them ripped from vinyl (my own plus crackly 78 rips from archive.org)...it's not like I'm expecting audiophile quality, but "good enough", especially just for a mixed CD to play at a party with people who are too drunk to care, or while driving. I just want it even so when I put it in I'm not babysitting the volume. That's all. 🙂

Another issue in the normalization process is what track do you use as a reference? If you have 50+ GB of songs, itunes would have to determine the PEAK volume of that song, then increase/decrease the volume of ALL of the other tracks to match that PEAK volume, which means determining the peak volume of every single track in itunes. Well, 50GB of music is a LOT of tracks. It would take days to determine this, and then go back and increase/decrease every living tracks volume individually to match.

::sigh::

yeah.

Burning a CD is different. There's only a few tracks to deal with. There is also a difference between NORMALIZATION and SOUND CHECK. Normalization raises the ampitude of each track to match a certain reference track (i.e. the loudest on the CD). Sound check just trys to get everything close the same volume.

Problem solved?

Oh...for the one that doesn't see anypoint in burning CD's: Sometimes ya just gotta, like, burn that downloaded album from iTunes music store so you can reimport it as MP3. some of us just need the compatibility with other audio programs...

Another issue in the normalization process is what
track do you use as a reference?

You don't use a track as a reference, you use an absolute reference level. Sound Check and ReplayGain both use a reference level of 89 dBm (dBm = power level in decibels relative to 1 milliWatt).

If you have 50+ GB
of songs, itunes would have to determine the PEAK
volume of that song, then increase/decrease the
volume of ALL of the other tracks to match that PEAK
volume, which means determining the peak volume of
every single track in itunes. Well, 50GB of music is
a LOT of tracks. It would take days to determine
this, and then go back and increase/decrease every
living tracks volume individually to match.

Actually, it would take less than a second to both determine this and to adjust every track in the library, no matter how large the library is. Why? Because the music files themselves are not being altered.

What SoundCheck does is to determine the "average" volume level for each track. This is not as simple as it sounds, as "volume" is subject to perceptual differences. That is, it's not a particularly simple matter of mathematics. High frequencies sound louder than low frequencies, even when the gain is the same. That sort of thing.

So once you determine the volume for each song, you then adjust it to match your reference level at the time of playback. Or, in this case, at the time in which you burn it. The original file remains unaltered, you're changing the sound as you process it instead.

You can also store peak information in order to prevent clipping, but I'm not sure if SoundCheck does that or not.

Burning a CD is different. There's only a few tracks
to deal with. There is also a difference between
NORMALIZATION and SOUND CHECK. Normalization raises
the ampitude of each track to match a certain
reference track (i.e. the loudest on the CD). Sound
check just trys to get everything close the same
volume.

No, that's actually not what "Normalization" does at all, really.

Peak normalization works by the simple expedient of adjusting the entire file by some percentage. That percentage is the maximum sample divided by the maximum possible sample. In the case of a CD, the sample size is 2 bytes, or 16 bits, and so the maximum possible sample is 32767 (it's a signed int). By adjusting it so that the highest sample is at this point, you get the maximum possible sound without clipping. Notably, peak normalization does NOT consider differing volumes between tracks, each track gets peak normalized independantly.

RMS normalization is more complex, but basically it has the effect of raising the quiet parts more than the loud parts, giving a better volume leveling effect. However, this also lowers the dynamic range of the audio as it is a form of dynamic compression. Really, this ruins the sound although most people think it's good because "it's louder" (sigh). Most commercial CD's you buy nowadays have quite a bit of overcompression applied to them. Annoying, really.

Oh...for the one that doesn't see anypoint in burning
CD's: Sometimes ya just gotta, like, burn that
downloaded album from iTunes music store so you can
reimport it as MP3. some of us just need the
compatibility with other audio programs...

There are better ways than burning CD's to achieve this. I refer you to the dbPowerAmp forums. 'Nuff said.