Digital audio is a topic that comes up quite frequently among computer users, and for good reason. There are enthusiasts who think nothing of buying the very best equipment and everyday users whose only consideration is audibility. Of course, there also exists the group which did not know it wanted to know about audio quality.
Files are generally assessed on their bitrate. A 320kbps MP3 is obviously better than a 128kbps version, right? Ordinarily, yes. But it’s not hard to bluff the bitrate and mislead listeners through “upscaling.” In fact, upscaling can sometimes damage audio quality.
Audio encoding is a complex process, and Stack Overflow user “vaxquis” provides an intricate explanation of how it works. If you find the subject interesting, his explanation is one of the clearest available.
How do you sort the wheat from the chaff?
Begin by downloading Spek, which is an acoustic spectrum analyser. Others exist, but we chose Spek based on its cross-platform compatibility and free nature. Spek is available as a portable file in a .zip; we explained the appeal of these programs previously.
Drag a file into the window for Spek, and wait a few moments as it draws a chart. At the bottom is the running time of the track; to the right is the track’s volume, and most importantly the frequency displayed on the left.
Essentially, bitrates work with frequency. Higher bitrates preserve higher frequencies. 320kbps cuts off at 20kHz, as shown below. The chart is for a track that is in 320kbps. There are meant to be exceptions, but since there are only a few standard encoders, this applies for the most part.
FLAC files don’t lose any of their higher frequencies, hence being known as a “lossless” file type. A true FLAC is shown below. For many audiophiles, there is little substitute to totally lossless audio.
Finally, take a look at this track. Note the fact it cuts off at 10kHz. That’s indicative of a 96kbps file, as that is where they cut off. Most people will be able to determine that a 96kbps file sounds poorer than most other bitrates.
iTunes disagrees when we confirm that the track is 96kbps. In fact, it believes that the song is 192kbps. In other words, it has been upscaled to appear as something it is not.
You can see the effect of upscaling quite easily if you play around with suitable software. We chose to demonstrate using Audacity; again, it’s free and cross-platform.
After first attempting to export an MP3, Audacity will inform you that it needs the LAME encoder. Download it and put it in a suitable location.
Return to Audacity and place an audio track into it.
Render the track as an MP3 and select “Options” during the “Save” dialog.
Finally, bring the song into your media player of choice and check the details. It is, ostensibly, a higher bitrate copy. Any improvement found will be a placebo – the original track never had the frequencies of a true 320kbps file and will not have been able to recreate them either.
Upscaling is easily done and can be highly misleading. Naturally, it sees most frequent use on illegitimate files. If audio quality matters even a little bit to you, there is no substitute for mainstream vendors like iTunes, 7Digital and Beatport or CDs.