DBX decoding

radio, tape, stands and accessories
Listenear
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DBX decoding

Post by Listenear » 11 Aug 2018 07:56

I have a technics RS-B207 DBX cassette deck & ask is there any way this could be used to decode - (playback), a DBX encoded LP ?
I'm not sure if originally DBX LP's had to have a dedicated RIAA stage separately, a special amp with it built-in, or whether there was a separate DBX add-on unit between the RIAA preamp & the main amp.

Can someone enlighten me please ?

Alec124c41
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Re: DBX decoding

Post by Alec124c41 » 11 Aug 2018 12:14

IIRC the DBX units went into a tape loop.

Cheers,
Alec

analogaudio
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Re: DBX decoding

Post by analogaudio » 11 Aug 2018 17:35

I cannot answer your question about the original hardware.

It is very likely that the encode-decode scheme used for cassette was different from that used for LP. An attempt to use one for the other may run into significant incompatibility problems, with degraded sound quality.

However you could try recording the LP on the cassette machine with encoding off, and then play back the recording with decoding on.

Listenear
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Re: DBX decoding

Post by Listenear » 12 Aug 2018 22:03

Thanks for your replies.

What I would like to do is just use the electronics of this deck to decode the DBX without actually recording it first, as I don't think that after all these years that it is all that flash via tape.

Probably impossible but, I would like to get an output from the playback DBX section only but I don't see a service manual on VE & likely not worth the effort.

However, it seems a bit surprising that originally Technics did not have a way of using all this technology on this deck to make it way more versatile & appealing sales-wise.

analogaudio
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Re: DBX decoding

Post by analogaudio » 13 Aug 2018 17:07

For service manuals for electronics try sister site HiFi Engine, there is a link at the foot of the page.

Listenear
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Re: DBX decoding

Post by Listenear » 14 Aug 2018 02:45

Thanks for your reply but there are no service manuals, only brochures etc for this model on these sites.

Does anyone know a site for a service manual for a Technics RS-B207 ?

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Re: DBX decoding

Post by Sunwire » 14 Aug 2018 04:48

I own a DBX 128 unit that has tape noise reduction and DBX disc decoding. It also has a variable compressor/expander/limiter/peak unlimiter. It's quite versatile, but I think the tape noise reduction and disc decoding are the most useful features.
I just reviewed the manual.
It says the DBX II encoding used for tape and LPs is the same.
Unfortunately, my look at the Technics RS-B207 brochure makes me think it will be impossible to use that deck for disc decoding. The only way it could work is to record the disc with no noise reduction, then play it back with DBX noise reduction engaged.

It might be possible to modify the cassette deck so a line level signal from a phono preamp went directly to the input of the DBX noise reduction playback circuit. But that would require some surgery. But probably not super difficult if you're handy with such things.

It looks like if you're patient you could buy a DBX 128 on ebay for as low as $50-60 or $100 if you're not patient. :)
Other DBX units might be even less. I didn't look.

Listenear
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Re: DBX decoding

Post by Listenear » 14 Aug 2018 11:09

Thanks Sunwire - (Like your Kitty !)

The surgery part doesn't really phase me but I would need a service manual & circuit before I'd look at modifying it.

Have you tried playing any DBX encoded discs ? - If so, how do they compare ?

Sunwire
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Re: DBX decoding

Post by Sunwire » 19 Aug 2018 02:18

I own a couple of dbx discs. I haven't listened to them for a long time and don't have the dbx unit set up at the moment. My memory is that the dynamic range was far better than for a normal lp, with no background noise, at all. But I'm not sure how it compares to a digital version of the same recording. I have Supertramp's Crime of the Century album and I think one other one I can't recall at the moment. Crime of the Century is very well recorded and quite dynamic, so it's a good album for the dbx format.

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Re: DBX decoding

Post by SpruceMoose » 15 Nov 2018 01:46

Dbx encoded albums are spectacular! Dead quiet. The first one I ever played, I set the needle down and didn’t hear any background noise. So I turned up the volume. I still didn’t hear anything so I turned it up some more. Then the music hit. HOLY CRAP!! Nearly messed myself! Boy did I turn it down fast.

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Re: DBX decoding

Post by Gravitar8 » 15 Nov 2018 23:36

Is there a benefit to using a stereo compressor/expander/limiter/peak unlimiter that does not have DVX decoding? I've been thinking about trying it as a pseudo noise-gate for LP playback. Just wondering how you use your unit's features for this and what settings work best... ps I have a newish DBX unit that has just been retired from a home studio.
Sunwire wrote:
14 Aug 2018 04:48
I own a DBX 128 unit that has tape noise reduction and DBX disc decoding. It also has a variable compressor/expander/limiter/peak unlimiter. It's quite versatile, but I think the tape noise reduction and disc decoding are the most useful features.
I just reviewed the manual.
It says the DBX II encoding used for tape and LPs is the same.
Unfortunately, my look at the Technics RS-B207 brochure makes me think it will be impossible to use that deck for disc decoding. The only way it could work is to record the disc with no noise reduction, then play it back with DBX noise reduction engaged.

It might be possible to modify the cassette deck so a line level signal from a phono preamp went directly to the input of the DBX noise reduction playback circuit. But that would require some surgery. But probably not super difficult if you're handy with such things.

It looks like if you're patient you could buy a DBX 128 on ebay for as low as $50-60 or $100 if you're not patient. :)
Other DBX units might be even less. I didn't look.

Sunwire
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Re: DBX decoding

Post by Sunwire » 17 Nov 2018 01:33

I don't use it at all these days.
A dbx model 3bx or 4bx might be more useful for what you want. They divide the audio signal into 3 and 4 frequency bands before applying dynamic range expansion. This reduces the artifacts ("breathing" sound) you get with a single band expander like the model 128.
Manuals are freely available online if you want to read about them.
I bought a 3bx a few years ago, but (like a lot of my equipment) it needs repair. ☺

JoeE SP9
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Re: DBX decoding

Post by JoeE SP9 » 17 Nov 2018 19:05

Unless specifically labeled on the front panel a DBX BX series device will not decode (expand) DBX encoded LP's.

The OP did ask about playing DBX encoded LP's.

Sunwire
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Re: DBX decoding

Post by Sunwire » 18 Nov 2018 02:11

I was responding to the question (not from the OP):
"Is there a benefit to using a stereo compressor/expander/limiter/peak unlimiter that does not have DVX decoding?"

And the answer is "yes". If you want to reduce noise on non-dbx records.
In which case, the 3BX or 4BX might be a good choice.
Both of them will work better to reduce noise on non-dbx records than the dbx model 128 will work for that purpose.

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Re: DBX decoding

Post by Gravitar8 » 18 Nov 2018 22:39

Excellent! I suspected as much having some experience using stereo compressor/expander/limiters in recording studio settings as forms of 'noise gate/triggers'. I will hook my unit up over the next couple of weeks or over the holidays when i have some time to play around. If you have experience with setting ratio,attack/release rate etc. please share :)
Sunwire wrote:
18 Nov 2018 02:11
I was responding to the question (not from the OP):
"Is there a benefit to using a stereo compressor/expander/limiter/peak unlimiter that does not have DVX decoding?"

And the answer is "yes". If you want to reduce noise on non-dbx records.
In which case, the 3BX or 4BX might be a good choice.
Both of them will work better to reduce noise on non-dbx records than the dbx model 128 will work for that purpose.

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