Dolby S – S is for surprise

After having watched Techmoan’s Cassette video I couldn’t resist and bought myself a cassette deck with Dolby S. In my case it was a Yamaha KX-580.

How I used to use cassettes

Before I bought a Minidisc recorder in 1996 or 1997 I used Metal cassettes, recorded them on my Telefunken twin deck and played them on the Alpine stereo in my car. The sound was usually fine, except the very annoying tape hiss you got all the time.

First impressions

My first impression with the Dolby S deck: Great! Much less hiss than I remember, despite only using a ‘Normal’ cassette. It was a Maxell UR 90 tape I had lying around, still shrink-wrapped. I think my wife got it when her previous university phased out tape recorders. Reasons for the better sound compared to what I remembered? I guess I either remember there being more hiss than there actually was, my ears got worse or my Telefunken deck or Alpine stereo had a problem – or maybe it’s a combination of all of these reasons.

Dolby S

I was however brought back down to earth when I tried did a comparison and tried out Dolby S.

I was expecting a lot – having watched Techmoan’s video my expectations were pretty high, but then there were also other documents, like this PDF, which doesn’t have an author, but seemed pretty well written and said things like:

“We have found that, at the highest playback levels likely to be encountered in the home, sophisticated listeners subjected to A/B comparisons of CDs and Dolby S-type cassettes are unable to identify which is which with any regularity.”


Dolby S-type Cassette Decks provide performance comparable to that of a Compact Disc, utilizing standard (Type I) blank cassette tapes.

There’s also this diagram in my cassette decks’ manual:

from the Yamaha KX-580 manual

It also gives the impression that Dolby S will outperform Dolby C in terms of noise reduction.

Reality / the test

What I got was very different though. For my test I recorded two songs from YouTube’s audio library on a new Maxell UR 90 cassette: Far Away by MK2 and I’m Fly by Gunnar Olsen. Both were burned on a CD-R and played back on my SEG DVD player (also available as a Yamakawa, these were affordable multi region DVD players from the 1990s that actually use an ATA DVD drive). I recorded the same two songs without Dolby, with Dolby B, then Dolby C, then Dolby S. I then played them back using the same type of Dolby used for recording, i.e. the Dolby B recording was played back using Dolby B, etc. and recorded the output using 96 kHz and 24 bit.

To my surprise the noise floor of the Dolby S recording was higher than that of the Dolby B recording. If you adjust the input levels for these songs, maybe slightly conservative, then the noise floor level without noise reduction is -48 dB, with Dolby B it’s -57 dB, with Dolby C -59 dB and with Dolby S -54 dB.

The cassette deck seemed to be in great condition, so I wonder whether something is broken or whether this is normal behaviour. It would be great to hear from you if you have a Dolby S deck.

Noise floor comparison

I put the recordings on YouTube, if you want to listen for yourself, but I should add that even though I recorded them with 96 kHz and 24 bit I had to use AAC with 48kHz and 320 kbps for encoding the video. I don’t know whether YouTube will then reencode the sound again. I guess what quality is sent to your machine will depend on the quality of your internet connection, so what you hear is only to some extent representative.

Here are the videos

No noise reduction

Dolby B

Dolby C

Dolby S


Techmoan also mentioned cassettes in his blog.


7 thoughts on “Dolby S – S is for surprise

  1. Tape quality is probably the biggest factor. I personally can’t tell any of the Dolby cassette formats apart. When I do it’s probably a placebo because I’ve been told S sounds a lot better. My first deck was a Technics with Dolby B in 1979. I think the biggest improvement in cassette sound was Dolby HX, S was only slightly better.

  2. This is a design fault in the 580 (it’s the same deck as the KX-480 with Dolby-S added as an after-thought).

    If you still have the deck, listen through its own headphone jack. Guess what? Dolby-S works as it’s supposed to, but NOT via the line-out. Yes, it’s bizarre, but I have TWO 580’s and both behave identically.

    The tapes encode properly, but listening via line out, only the sub-1KHz noise is re-expanded (LF and any mains noise that might have got into the signal path) but not the hiss (remember that all the analogue Dolby systems are “companders” – they compress on record and expand on playback).

  3. Oh, and BTW, re. Youtube uploads – I’ve found that for ordinary user accounts, the audio is transcoded transcoded to AAC 44.1KHz @ c. 100-128kbps. Some “official” uploads seem to be at c.192kbps.

    Anyway, it’s a good idea to record your audio at 44.1KHz and use high-bitrate AAC (256, maybe 320), given you’ll probably be using MP4/x264.

    1. Thank you for this explanation. This is great stuff.

      I did observe some odd behaviour with the headphone out. I think it had to do with the line out volume being different depending on whether a headphone was connected or not, but I don’t remember the details. What a shame the 580 has this fault.
      I recorded it uncompressed with the highest setting my Zoom recorder had but had to use AAC for uploading.

      1. Well, it get’s even stranger. I was just recording a few samples to demonstrate the above-metnioned headphone vs line oddity and discovered that Dolby S (on the 580 I currently have in my system) has decided to start working properly.

        The unweighted RMS noise figures for B, C and S respectively are now -63dB, -69dB and -78dB. These were obtained after peak-normalising recorded material to -1dB.

        There’s no question that I was experiencing exactly the same thing as yourself. I discovered it only a couple of weeks ago when I was recording a 3150Hz tone for speed testing, and wanted the noise-floor as low as possible – which is to say, slightly more hiss than with Dolby B.

        I wonder if there’s something amiss with the logic circuitry in these decks. Notice the odd button layout – one button to step through B and C and a separate one for S (you’d expect a single button, or even separate ones for each of them). I wonder if it gets ‘confused’ by certain combinations of presses on them?

  4. Forgot to say – I also happened to be using the same tape you had to hand – recent-ish Maxell UR. It’s not as good as it was back in the day (probably not the same tape at all, in fact). Those impressive-looking noise figures were obtained after having probably over-done the levels with the stuff I was recording for a reference level – regularly lighting-up +3 on the meters, I’d generally keep cheap ferric like this out of the red altogether.

  5. Sigh. Well that didn’t last long. I just HAD to run a couple more tests today, and Dolby S is misbehaving again. Measured noise (raw RMS) has gone back up and is obviously audible, yesterday it rendered the tapes practically silent (I kept the recordings). I still suspect it’s down to the logic/switching – some combination of powering the deck on/off, tape-tuning and stepping through the Dolby iterations.

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