How to spot a transcode

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This topic contains 6 replies, has 6 voices, and was last updated by  Anonymous 3 years, 1 month ago.

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  • #2661

    mojib
    Keymaster
    @mojib
    Level S

    Knowing if your audio files are transcodes or not isn’t always easy. You need to analyze the audio spectras.  The recommended software are Audacity, Audition, and SoX (Spectro and Spekhave potential for analyzing transcodes too). Note that Has it Leaked doesn’t require an album to be a non-transcode in order for it to be reported as “leaked”.

    Since this topic is related to different formats and bitrates I recommend reading this blog post, which has the original guide from a former audio bittorrent site called OiNK. I would also recommend this topic concerning how to read spectrals.

    One of the more interesting and simpler way of telling if an audio file is a transcode or not comes from the user “brigetd”.

    How to interpret the frequency spectrogram of songs

    I’ve seen a lot of discussion here about how to spot transcodes. Many people have suggested using a spectral analysis from programs like Cool Edit / Adobe Audition and looking at the “cut-off” point. There is some disagreement about how effective this is, but those who recommend it suggest looking for cut-offs between 16 kHz (as the signature of a 128 kbps MP3 source) and 22 kHz (i.e. no cut-off at all) as the signature of a lossless source.

    One counter argument to this “cut-off” level method is that the same cut-off that characterizes lossy encodes may also be the result of a poor quality recording – a bootleg of a live show or a “third world” vinyl master.

    A number of spectral views have been posted and linked to but nearly all of these have been analyses of entire tracks… which IMHO is NOT the most effective way to use spectral analysis to detect transcodes.

    What I haven’t seen anyone discuss is the “blocky” appearance of the frequency spectrogram of lossy rips, which is noticeable only when you zoom in close enough. IMHO this is a more reliable way to detect whether a file, which purports to be lossless, has in fact been transcoded from a lossy rip, and may even be a useful way to detect re-encodes from lower to higher bit rate MP3s (although this is much harder whatever method you use). However, some consideration of the source material is necessary here as well. Electronic music, for example, frequently makes use of instruments that use the same technology as lossy audio encoding, so a blocky appearance in the spectrogram might be normal for a lossless source under certain circumstances.

    The image below illustrates what I mean. The track (from an album by Philip Glass) was ripped from CD to FLAC and a 1-second sample was saved to 320 kbps LAME MP3 and 128 kbps FhG MP3; and then in each case saved again to FLAC. The spectral analysis was done at full screen on a monitor with a resolution of 1280 x 1024. Each of the three strips below is of the same 0.15 second interval in all three audio files.

     

    FLAC / 320 MP3 / 128 MP3 compared


    And here are bigger strips of the three spectral analyses. The zoom level is the same – bigger simply means that what is shown here is around 0.5 seconds – and NOT the whole track!

     

    FLAC

     

    320 kbps LAME MP3

     

     

    128 kbps FhG MP3

     

    #10411

    Austin
    Participant
    @audiobinge
    Level 6

    Anyway to have this pinned so it’s more visible in the forums?

    #43687

    Aidan
    Participant
    @xvulnerable
    Level 4

    Wait, so is FLAC or 320 Kbps better?

    #57722

    paranoid
    Participant
    @noseeds
    Level 6

    Flac is the best.

    #101128

    Eric
    Participant
    @electronic-blue-whale
    Level 3

    What an excellent post. I’ve been looking for something similar for a while and nothing has been as clear and simple. I second the recommendation to have it pinned. Or better yet combining it with the “Transcodes” thread. That thread had a lot of useful information as well.

    @Aidan

    Wait, so is FLAC or 320 Kbps better?

    The FLAC format is considered lossless, which means you don’t lose any quality from the original source. If the files came from a CD the FLAC files will be identical to the original CD audio. The MP3 format is lossy, which means you lose quality from the original source. A 320kbps MP3 will sound better than lower bitrates but any MP3 means there is a loss in quality.

    At higher bitrates most people cannot tell the difference between an mp3 and the original full quality audio simply by listening. That is why guides like this are so helpful.

    #143323

    Austin
    Participant
    @audiobinge
    Level 6

    256 is okay for me. Depending on the type of music 120 is even all right but after that it takes a huge nosedive for me. Some old Blood Brothers demos from ‘Crimes’ are like 78-90 on my computer and if it wasn’t for my love of the band and the track rarity, I’d completely hate them.

    #182871

    Anonymous
    @
    Level 0

    That is a meticulous task, accuracy needs to be in perfect ratio.. also a process in dubbing and narration, transcoding sounds to voice should match by milliseconds accuracy. If you need expert on this, try http://www.debbieirwin.com/, surely they can help you.

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