Simple comparison of lossy formats: tape vs MP3

It’s another horrible wet night, so let’s compare a tape recording to a MP3 rip just for some fun. The track chosen was the beautiful Natalie Imbrulia single ‘Wishing I Was There’ from the CD album ‘Left of the Middle’. The exact same song was treated in two different, yet profoundly simple ways.

The cassette recording was recorded from the CD album to a Japanese metal position tape and encoded with Dolby B noise reduction, invented in 1968. A well maintained & aligned portable Japanese portable boombox from the 1980s was used for the recording.

Once recorded onto the tape, the song was played back on the same machine into a Yamaha DS-XG sound card to convert from analogue to digital. On the computer, Total Recorder was used to create a digital uncompressed PCM recording.

In Audacity, digital noise reduction was used to remove any residual hiss present in the uncompressed recording. Hiss is rarely audible with metal tape recordings, but as it takes all of one minute to do, why not be thorough when forced to use Dolby B noise reduction?

Dolby C is roughly ten times more effective than Dolby B noise reduction at minimizing audible hiss & maintaining wide dynamic range. Decks with Dolby S noise reduction provides CD-grade signal-to-noise ratios of 90 decibels, which are indistinguishable from the original CD source.

Ghost in the Machine: Jim Morrison

Don’t worry, in the event this simple comparison of lossy formats gets too boring (too late?) just focus on the amazing cassette art from New Jersey artist Erika Iris Simmons, above and below!

On a computer, a MP3 file was extracted from the CD album using CDex software. The MP3 was encoded using LAME version 3.99 using the highly-rated 192 Kbps Variable Bit Rate (VBR) encoding (192 Kbps is the average rate of the musical recording). Use of VBR mode maintains a uniform signal-to-noise ratio. Again, Total Recorder was used to convert the MP3 recording to uncompressed format.

Ghost in the Machine: Nick Cave

Both uncompressed tracks were ‘normalized’ to a peak amplitude of 0 decibels. The stereo channels were converted to mono to aid visual comparisons. Head-to-head, the two candidates are pictured below.

Pictured below, the response of the spectrum audible to humans (20 Hz – 20 kHz) is wide and fairly uniform. As we compare the amplitude in decibels with the frequency response in Hertz. The boombox tape recording of the CD track shows a robust high frequency response. High frequencies begin to gently roll off above 15.5 kHz. Between 11-14 kHz there is not much content in this particular track. High frequencies begin to gently roll off above 15.5 kHz. The music range extends beyond 22 kHz.

On a good quality component cassette deck, with adjustable bias & Dolby HX Pro headroom extension, the high frequency response would likely show less deviation & start to gently roll off at around 20 kHz rather than the 15.5 kHz roll off visible below. On the audiophile-grade decks, such as the Nakamichi Dragon of the late 1980s vintage, the differences between the CD source material and the tape recording are reportedly indistinguishable, according to tests in Electronics Australia.

Let’s remember that a consumer-grade portable boombox was chosen for this test. This test is not about achieving transparency (that is, a virtually perfect duplication of the source). It’s far more interesting to illustrate the differences between simple lossy analogue & digital formats!

Turning our attention towards the MP3 copy of the CD track, below, the response of the audible spectrum is again wide, yet in some ranges slightly more uniform than the boombox tape recording. High frequencies start to sharply roll off above 16.5 kHz, slightly higher than the boombox tape recording. There is also less variation in the content from 6 kHz onwards. Consistent with the tape recording, there is emptiness between 11.5-14.5 kHz. There is no content after 18 kHz, a characteristic of digitally compressed audio. In his research for his masters degree, Chris Camilleri found that compressed audio changes the frequency response in the following manner:

 

192 Kbps MP3 was chosen because it is a popular bitrate for music downloads that provides good quality transparency. 192 Kbps preserves significantly more high frequency material than FM radio broadcasts do. On MP3 recorders such as the Samsung Yepp, 192 Kbps is the maximum allowable bitrate for encoding. For Audiophile-grade encoding, 320 Kbps MP3 is recommended.

Additional discussion

Home Recording. A comparison of tape vs MP3 by a New South Wales-based musician.

Melissa Clarke. A history of Vinyl vs Tape vs CD vs MP3. By a Queensland-bred music journalist.

Child of the Eighties. A history of Vinyl vs Tape vs CD vs MP3. By programmer Big Boo.po

The Guardian. How much difference is there between MP3, CD and 24-bit audio? By Samuel Gibbs et. al.

This entry was updated in August 2014.

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