[geowak]

About 9 months ago i copied my ITUNES library of about 10 thousand songs from a desktop external HD to an portable external HD. I wanted to take the external HD with me on a long trip.

Both the HDs are made by IOMEGA. The computer with the Itunes is an older Apple EMAC.
The files are AIFF files.

Well here is the odd part that I cannot figure out. After i listened to the music on the portable external i noticed the music had been altered ever so slightly. If anyone has ever used a variable pitch/speed turntable you know you could turn the knob and the speed of the platter would increase or decrease the playback sound/speed of the music depending on what you wanted.

Well the music on my HD has been pitched SLOWER. It is not much, but since the music on the HD is music I LISTEN TO AND KNOW, I can tell it is slower. Does anyone have any idea what happened in the transfer process that could have caused this??

[JohnR]

Wonder if the sample rate (metadata) was altered somehow. Are you able to access both copies of the library at the same time (e.g. one on the desktop and one on the laptop) - then you could compare what iTunes thinks the file info is.

[jtwrace]

Wonder if the sample rate (metadata) was altered somehow. Are you able to access both copies of the library at the same time (e.g. one on the desktop and one on the laptop) - then you could compare what iTunes thinks the file info is.

What would you look at though?   

[JohnR]

Wonder if the sample rate (metadata) was altered somehow.

... the library xml file could also be opened directly. Plus, then the same song could be played from both libraries at the same time to confirm that the tempos really are different.

Just a suggestion... 

[Quiet Earth]

You know what? I think you are a good listener geowak.

I think what you are describing is a good example of what plagues digital music and especially computer audio in general. The copy, or the transfer of "data" can be considered to be executed perfectly by the computer, yet the timing of the music that resides in that "data" is irreparably corrupted forever. No amount of jitter reduction or after market solutions seem to fix the root of the problem.

I think we still have a long way to go to get the most out of digital music. Especially computer based audio.

[wilsynet]

Nothing happened in the file transfer process between portable and non-portable drives.  If you were to compare the files between the portable external and the non-portable external drives, they should be identical.

One experiment that you could do is to take one of those files on the portable external and copy it to the non-portable external (rename while doing so).  The two files should be identical and sound the same playing from the same media.

Having said that, Quiet Earth is certainly right that there are timing considerations.  Where the timing considerations come into play is clocking the data in, decode, transform, etc. and then clocking the data out.  That is, the bytes that are in a music file, whether AIFF, WAV, MP3, etc. must be read in, translated into something appropriate for a DAC, then written out to the DAC for ultimate conversion to analog.

Here's what I think may be going on:

The portable drive has a different tax on CPU load than the non-portable drive.  Different devices will incur different penalties.  For example, the portable drive may be able to transfer data less efficiently and hence requires that the CPU provide more service to transfer the same amount of data.  No surprise here: the portable device is being built with tighter requirements on size and packaging with more forgiving requirements on performance.  One way to think about it is: if you had to fetch two pails of water from the well, wouldn't it be easier to make one trip with two pails in hand rather than two trips with one pail in hand?  The portable drive by way of analogy may only have one pail to work with, and that means the CPU needs to make two trips instead of one for the same two pails of water.  That's more work for the CPU.

The impact to the CPU (as marginal as it may be in the grand scheme of things) would affect the overall lifecycle of reading, processing and sending to the DAC.  This is fundamentally a real time activity as it pertains to the stage where the data is clocked out to the DAC for analog conversion.  The more the CPU is interrupted with the need to service other activity (such as fetching another pail of water from the portable drive), the greater the affect on the final result.

It seems unlikely that fetching an additional pail of water is the sole reason for the difference, but I would certainly understand if the portable drive required more processing time and more interruptions in general.

[jrebman]

I believe Wilson is right on the money here.  The Iomega external drives seem to be somewhat slower than the other drives that use oxford chip set, and usb seems to have more overhead than firewire 800 and obviously more than your internal drive.

I'm not slamming iomega drives -- have several of them around here for archival drives, but in general they are too slow for realtime audio use.

-- Jim

[jtwrace]

I find this odd as Gordon Rankin actually suggests using iomega drives and he really knows his stuff. 

[jparkhur]

I have my itunes lib on my HD, plus backed up to a Seagate drive, plus a monthly apple back up to my time machine drive.  I have taken my back up down to my receiver and used it as a usb driver to play music off of and NOT had any issues with it.  Wonder if the drive at the time was slower??? Something appears to have happened to your copy?  Can't say that I have heard of that either.

450 gigs, 34,000 songs.  No issues so far

[avta]

You might try copying one of the files from your original drive to a flash drive then play it back from there and see if you still hear a difference.

[davidR]

When you said your source with Itunes was an old emac the red flag went up for me.  Sounds like your computer is struggling with the USB transfer from the portable drive. Both the age of your mac and the specs on your portable drive are certainly factors at play concerning this type of issue. Try copying one of the music files from the portable drive and playing it back from the internal hd on your Mac. If it plays at the proper speed you know it's not the actual file itself but a hardware issue. Just so you know I've had this type of issue on my 8-core Mac Pro when playing music externally and loading files on the drive at the same time just fiddling around to see if I could get hiccups during playback. I think a general consensus among people is that you can use any old computer for computer audio and it's just not that simple. Sure the processing overhead is pretty low for today's current systems & technology simply playing back music files but there's many other factors at play. Throw an older computer (just from a few years ago )into the mix and stream data in real-time and it's almost asking for issues. What exact model of the Iomega portable hard drive do you have? I highly recommend the Glyph PortaGig series drives.

[geowak]

Davidr

I actually thought about the possibility of a usb transfer issue. When I setup the music files transfer, I could not get the Mac firewire cable to work so i used the USB cable. The transfer took a long, long time to finish. I cannot do some tests right now, but I am going to time the playback duration of two songs of the same artist. One played with a CD player and one played via my ext HD. This will verify just how slower the playback of the song on the HD has become.

[minotaur]

To at least see if the files are different due to copying between the different drives, you can try to do a sha1 digest on the files themselves.

here's an apple support page that details the procedure: http://support.apple.com/kb/ht1652

This way you can at least know if the files themselves are different.

Please let me know if this is confusing at all.

[APro]

The speed of the I/O, in this case the USB drive, will not affect the playback speed of the AIFF file.  The data will be read into a buffer, and played from the buffer.  If the drive cannot keep up with the demand of the music player, you would get either a 'buffering' message, just like some internet radio stations, and the music would play intermittently, or you might see disk/file errors.

Any data corruption to the files would result in dropouts and glitches in the sound.

What release of:

  iTunes
  Mac OS X

are you running, and, what are the specs of the computer.  Also, what is the bit rate/frequency of these files.

Oh, one more thing.  If you play a CD on the Mac, does it sound right?