How to Check the True Bitrate of Your Audio Files

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.

Bitr-Spek-UI

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.

Bitr-320kbps-Audio

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.

Bitr-FLAC-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.

Bitr-LowQuality-MP3

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.

Bitr-Cruiserweight-FalseReading

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.

Bitr-LAME-Needed

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.

Bitr-Track-Audacity

Return to Audacity and place an audio track into it.

Bitr-MP3-Options

Render the track as an MP3 and select “Options” during the “Save” dialog.

Bitr-Cruiserweight-FalseReading

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.

12 comments

  1. The cutoff ( “hard” in CBR and “soft” in ABR/VBR) frequency and the bit rate are independent, they use presets so there is a correlation between the two, impossible to achieve lossless compression with MP3, what is lost is the higher harmonics of the base frequencies. The 320 kbps version default is the stereo mode and default for 128 kbps is joint stereo. AAC achieve much better quality than MP3, at the same bitrate an AAC file of 96 kb/s sounds like a 192kb/s MP3 file. the OGG is the best solution for storage and listening of low bit-rate compressed digital audio.

  2. I am confused!
    Where or when did Audacity do the upscaling?
    I have been using Audacity for many years, but I never use joint stereo; only stereo.

    My audio files bit rate appears in the players just as it was set in Audacity Options.
    I use a number of players, but I don’t see any upscaling.
    Please clarify the step(s) where upscaling took place, if it did.

    Also, is there a list of the cut-off frequencies for the various rates? I would think such a list would be nonlinear.

    • Hi Googlian,

      I should point out that Audacity does not ‘upscale’ the audio quality in any way. It can, however, be used to give the impression of a higher quality file. The sound improvement is only ever going to be a placebo, though. iTunes and other media players will report the file to be 320kbps, although it has absolutely none of the benefits of a true 320kbps file.

      As for the cut-off frequencies, I’m not sure of a totally accurate list. There are a few popular encoders, and their frequency cut-offs seem to be the most popular. I suppose the most popular option is the LAME encoder, so if you can find its limits then you’ll have found one of the more trustworthy scales.

  3. I know that, Paul. I know that Audacity doesn’t do upscaling.
    I also know that once an MP3 is at a certain bit-rate, you can’t add quality to it by the fake upscaling, but you can reduce it, of course (downscaling).
    I have been involved with MP3 and other digital sound areas since the early 1990’s.
    LAME is awesome. Once of the best out there.
    I rarely ever find any “perceived” sound enhancement above 192 ks/s, although I encode at 225 ks/s usually.
    Thanks for commenting/replying.

  4. Hi, maybe someone can help me out. I have some MP3 files with a bitrate of 320kbit (CBR). So they should have their frequency cut at about 20-20.5khz. Now Audacity tells me, that the frequency cut is at about 21.5-22khz on those files, so it’s about 1-1.5khz more than it should be. 21.5-22khz is FLAC or Audio CD and not MP3. How is this possible, that 320kbit/s (CBR) files have that high freqeunciey accodring to Audacity? Any ideas? Itunes tells me, that the codec on those files is “unknown”.

    • Hi Brian,

      Those MP3s sound like they might not have been created with the LAME encoder. There are a few other codecs out there; some of them may have a slightly higher peak though I couldn’t tell you with absolute certainty. Definitely give it a search on Google and see what you can find: I did take a look but there are some very advanced discussions that, if I’m honest, go a little bit over my head.

      Sorry I can’t be much help with this one Brian, but I appreciate you getting in touch to share your findings.

      Regards,
      Paul

      • Hi, no worries. I googled about it for hours, but the only thing i could found is that 1 guy told in a forum that there is a Codec out there which possibly could go over the 20.5khz, but without any other details to that. As this was the only thing i could found, i wasn’t sure if he’s been right. I found 2-3 other posts were was spoken about to manually set the Frequencies to a Range over 20.5khz while converting with Lame, which usually doesn’t make no sense. So i was curios to thave such files in my collection. But thanks anyway for your reply.

        • Brian,

          When using LAME encoder on default settings it will cut off at something like 20.5 but there is an option where u can chooose your own cutoff points or even disable it altogether. I always disable it myself and usually end up with mp3’s that cutoff around 21-22 just like u described so that is most likely the reason. Also it should be noted that I use an older version of LAME and i’ve read that newer versions (i believe it said version 3.97 and up but im not sure) no longer allow you to disable the cutoff point. I run version 3.90 and i do know for a fact u can disable it in that version.

  5. Hey I’ve downloaded SPEC and some of my apparent 320kbps files are running around 16k frequency! Does this mean they are not truly 320kbps?
    Cheers
    Harris

  6. Hello Paul:
    I always use Spek everytime that I download an audio file, and I think it´s very reliable. However, I have a doubt about the range or spectrum shows. Some FLAC files shows a accentuated flat line (from left to right), denote apparently the Khz limit; but the range exceeds that flat line and reach the 20 or a little more Khz. Why is that?. I´ve read that situation means the FLAC audio is fake and it´s tampered. Coul you tell me your make of abour that?.

  7. Hello Paul:
    I always use Spek everytime that I download an audio file, and I think it´s very reliable. However, I have a doubt about the range or spectrum shows. Some FLAC files shows a accentuated flat line (from left to right), denote apparently the Khz limit; but the range exceeds that flat line and reach the 20 or a little more Khz. Why is that?. I´ve read that situation means the FLAC audio is fake and it´s tampered. Coul you tell me your make of about that?.

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