dbx 187

Never used one but I think they were used in studios to reduce tape hiss etc before the Dolby units became standard.  Not a bit of gear that has much use these days.

S

edit - way before my time


Edited by Sheggy - 29 October 2009 at 1:11pm

Dbx used to make some nice pro-audio back ine '70s,it was pretty expensive back then too,nicely made..here is a photo of a load of DBX rack gear (on the left hand side,black fronts with silver knobs.....actually the sliver knobs on these were a work-of-art by themselves,beautifully made from polished cast alluminium!)

Didi you get this Yardie -

www.audiorents.com/library/userManuals/1_dbx_187.pdf.

No it's not a noise gate (and it wouldn't accept a mic directly as it doesn't have mic inputs; could be used as a line insert device or perhaps aux sends etc).

I had a look through the manual which makes some quite big claims for it's effectiveness in tape transfers and on telephone lines of all things.  They say it is based on sequential compression and expansion which I think is very different to Dolby NR.  Makes it quite an interesting unit and it probably cost a small fortune in its day.

It's likely that studio engineers used it for things other that tape-to-tape; the manual mentions reducing noise on delays and reverbs (some of which were prone noise). I would play with it if I were you - see what it does to the sound.  You may even find some creative uses for it.

Some veteran pro audio dude will know much more about this than me. Hang on to it.

S

The DBX 187 is a noise reduction system for tape based recorders.

 

It doesn’t work like Dolby, which adds either 10dB (Dolby B) or 20dB (Dolby C) of HF boost when recording to tape then cuts by either 10 or 20dB when replaying back from tape. So if you boost by 10dB then reduce the HF by 10dB on play back you have also just reduced the tape noise by 10dB.

 

The early DBX system worked on compression. You can get more signal onto the tape by taking away the peaks and lowering the dynamics. When the tape is replayed the signal then gets expanded so the dynamics are the same as before they were encoded. If you can get 20dB more signal level to tape, then you will get a 20dB reduction in tape noise.

 

I had a 24 channel system I used to use on a 24 tr tape machine, but it was a newer model that the 187 and also applied HF boast and cut as well as compression. You have to have a very accurate and well setup tape machine to use any of the DBX noise reduction systems as if the tracking is out the expansion will not follow what the compression was and the sound will pump like mad. It also makes it difficult to plat DBX encoded tapes on other machines as they might differ in either output levels or quality. Dolby never had this problem. One point of note is that with my 24 tr machine running at 30 ips with the DBX system in place I could get 136dB dynamic range. Which is enough to record the quietist squeak of a kick drums pedal to a large man slamming down on the pedal. It’s also enough range to capture the quietist whisper to the loudest scream of a vocalist. Not many systems today can boast the kind of dynamic range.

 

So no, you can’t use the DBX 187 with a mic as a gate. You have to connect both inputs and outputs to a tape machine and encode when recording to tape and decode when playing back from tape for the noise reduction system to work.

 

Does this make me an old veteran dude because I know this ha ha.

Rog Mogale wrote: The early DBX system worked on compression. You can get more signal onto the tape by taking away the peaks and lowering the dynamics. When the tape is replayed the signal then gets expanded so the dynamics are the same as before they were encoded. If you can get 20dB more signal level to tape, then you will get a 20dB reduction in tape noise.