Dolby B, C and S Noise Reduction - Need To Understand... [Archive] - Audio & Video Forums

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Modernaire
04-13-2006, 11:57 AM
Hello everybody,
I'm sort of a novice in this department but here we go. My situation: I recently attained a Sony TC-WA7ES dual cassette deck with Dolby B, C and S Noise Reduction.

I got it in like-new condition. I lucked out because I previously owned the same deck used and with head cleaning and demagnetizing, this previous one sounded bad. I laughed at S NR thinking it sounded incredibly muddied and I didnt understand the fuss.

BUT I got this like new hardly if ever used deck and it sounds A-mazing.

Anyway, I got the deck for a large cassette to minidisc/mp3/CD-R project. I have tons of private recordings and cassettes are taking too much space.

Now, I recorded a song from original retail tape to my hard drive. Its an out of print/not available on CD cassingle from way back of a favorite song. Again, sounds fabulous with C AND S NR in playback. I used Soundtrack Pro with an iMic thing connected to a Mac via USB, you know the deal, to record as an AIFF audio file.

I'm comparing the recorded first parts of two separate recordings I made as AIFF files. One was with C NR and the second with S NR. I'm looping just the beginning silent part to compare noise reduction with iTunes. Great for comparisons. I just have both songs looping back and forth.

Here's the interesting part about my computer recordings. I hear the same hiss amount, although minimal, but when I push the volume up I dont hear one quieter than the other.

There is a slight difference in supression of higher freqs for the S which just barely cuts out the crispy highs of a hi-hat etc. But its still pretty good. My surprise is that I would think S NR would of cut that hiss but its coming through the same as C NR.

I'm sort of baffled. When I insert a retail cassette and switch from say B to C theres a big difference and I also hear the diff from C to S NR. This is of course just via the amp and not the computer.

I thought S would cut out the highs in the output so I could hear that difference in a computer based capture/recording? I just want to capture with the best NR and avoid using that nasty NR in the software.

Can any experts explain what may be happening or am I just too newbs for to understand the purpose or USE of B-C-S Noise Reduction.

Thanks and very sorry for the long post :o

Woochifer
04-13-2006, 03:11 PM
The short answer is that during playback, you simply need to use whatever version of Dolby NR was originally used in taping that cassette. If the tape was recorded using Dolby B, then you'll get the best results by playing it back with Dolby B. If the tape used Dolby C while recording, then you should use Dolby C during playback.

The thing to keep in mind is that Dolby B is the de facto noise reduction standard with the cassette format. Almost all commercially produced prerecorded tapes used Dolby B, and basically all tape decks made in the past 30 or so years have come with Dolby B.

When Dolby C came along in the mid-80s, it was touted as a system that was backwards compatible with Dolby B (but the reality is that the two systems sound very different). It made a big improvement in the noise reduction and signal-to-noise ratio. On my Aiwa deck, I thought that Dolby C cut out the noise, but also made the sound more abrupt. When playing a Dolby B-encoded recording using the Dolby C position, the highs sounded more prominent but artificial. In general, I kept recording with Dolby B because it simply worked better with my portable players and car deck.

Since you're using your deck primarily to transfer old cassette tapes to digital formats, I would stick with Dolby B, because in all likelihood, the recordings were originally encoded using Dolby B. Even though the tape noise is more audible, the music itself will likely sound closer to how it's supposed to sound by playing it back in Dolby B.

Also, keep in mind that the performance of the different Dolby noise reduction circuits can vary because these are analog circuits, with more audible differences than decoding/encoding circuits that process the signal in the digital domain. I remember people I knew who did a lot of listening comparisons on tape decks complaining about the audio quality on a lot of the combo Dolby B/C circuits compared to dedicated Dolby B circuits.

Dolby S is the consumer version of Dolby SR, which is extensively used with professional analog tape recorders. It's supposed to be a high performance noise reduction circuit that maximizes the signal-to-noise ratio and increases the dynamic headroom possible with the signal. It does a lot more with the signal than Dolby B or C, which basically work by selectively boosting the signal at specific frequencies, and then cutting the signal back at those same frequencies during playback. But, in order to gain any benefit from Dolby S, the original tape recording has to be encoded using Dolby S, and played back using Dolby S.

If you're looking to make your own tape recordings and test the different formats, rather than listening for tape hiss to compare the different formats, what you should actually focus on is which recording sounds closest to the original source in level-matched comparisons. In general, the Dolby S recording should give you the most accurate reproduction, and the tape hiss should be less of a factor when using Dolby S because you can use a higher level without the signal distorting.

daviethek
04-13-2006, 04:30 PM
My wife wants me to tape her favorite FM broadcast and burn them to CD's. Problem is, I haven't had a tape deck in 10 years. Are there any our there for a buck and an half and also, would the Dolby S help in taping FM? Gracias. dk

Modernaire
04-13-2006, 10:11 PM
Wow. Thank U Woochifer!

You pretty much schooled me, I still have to go back and do a double read.

I had a bit of time tonight and realized that as for C and S NR comparison, S pretty much reduces similar to C BUT the dynamic range seems to be lower. The highs sound nice but a bit supressed. Also the overall level output in S seems to be lower. I found I had to boost the volume to match what I heard with C.

And C NR seems to me to have a slightly higher dynamic range but again with the same NR as S. Interesting. S to me gave a more intimate effect on some recordings that of course were not recorded with S.

B does allow more noise and I had an idea that retail tapes that noted B NR should be matched up.

I think at least for me that C is the best. It clears out the noise/tape hiss a bit and still has a closer dynamic range to B or no NR. But when I want to enjoy a deeper more intimate version of a recording, S is the letter! I'lll be using the deck mostly for playback. I record prime on MiniDisc or CDR with an occasional MP3 rip.

I really appreciate your knowledge sharing and Im so glad to be a member of the Audio Rev community!

C > :0: < S

Modernaire
04-13-2006, 10:15 PM
My wife wants me to tape her favorite FM broadcast and burn them to CD's. Problem is, I haven't had a tape deck in 10 years. Are there any our there for a buck and an half and also, would the Dolby S help in taping FM? Gracias. dk

Hm, on my SOny ES deck it has an setting where you choose the FILTER which is for taping off of FM broadcasts.

Woochifer
04-14-2006, 08:52 AM
Wow. Thank U Woochifer!

You pretty much schooled me, I still have to go back and do a double read.

I had a bit of time tonight and realized that as for C and S NR comparison, S pretty much reduces similar to C BUT the dynamic range seems to be lower. The highs sound nice but a bit supressed. Also the overall level output in S seems to be lower. I found I had to boost the volume to match what I heard with C.

And C NR seems to me to have a slightly higher dynamic range but again with the same NR as S. Interesting. S to me gave a more intimate effect on some recordings that of course were not recorded with S.

B does allow more noise and I had an idea that retail tapes that noted B NR should be matched up.

I think at least for me that C is the best. It clears out the noise/tape hiss a bit and still has a closer dynamic range to B or no NR. But when I want to enjoy a deeper more intimate version of a recording, S is the letter! I'lll be using the deck mostly for playback. I record prime on MiniDisc or CDR with an occasional MP3 rip.

I really appreciate your knowledge sharing and Im so glad to be a member of the Audio Rev community!

C > :0: < S

Like I said, when Dolby was first pushing Dolby C, the equipment manufacturers were claiming that it was backwards compatible with Dolby B. But, in my listenings where the reference is the original source, I found that if the recording was originally encoded with Dolby B, it sounds audibly closer to the original source when played back using Dolby B. Dolby C made some changes to the tonal balance that I did not like.

I think you should try making some of your own tapes and then do A/B comparisons with the original source, so that you can hear for yourself how the different Dolby NR formats affect the signal. You should also try making a recording with no noise reduction. You might be surprised by what you hear (the tape hiss affects the dynamic range, but the tonal balance and transparency to the original source in many ways is more accurate when the noise reduction is turned off).

Nothing wrong with picking and choosing the NR format that sounds best with a particular recording, but comparing to the original source is the way to go if you want to identify exactly what the different NR formats do.

The noise reduction you're talking about for FM broadcasts sounds like the old MPX filters that a lot of receivers used to include. Unlike with Dolby NR, there was no standard format associated with that feature. The implementation varied by manufacturer.

royphil345
04-15-2006, 12:51 AM
My wife wants me to tape her favorite FM broadcast and burn them to CD's. Problem is, I haven't had a tape deck in 10 years. Are there any our there for a buck and an half and also, would the Dolby S help in taping FM? Gracias. dk

If you want CDs... Why the cassette deck "middleman"? Wouldn't you be better off just recording to CD quality files on your computer hard drive or stand alone CD recorder?

If easier editing is an issue, consider getting a good quality sound card and recording CD quality to your computer's hard drive for easy software editing, or getting a stand alone recorder that will record rewritable CDs. Either way, you'll spend less than you would on good quality cassette deck and get better results without buying any obsolete equipment. Could also pick up a cheap eBay tuner if your system is too far away from your computer for easy hookup.