Digital Processor Reviews

dbx 700 digital audio processor Specifications

Sidebar: Specifications

Description: Rack-mount digital audio processor using predictive delta modulation with compansion (CPDM). Output: conventional TV signal (North American standards) which can be recorded on any high-quality VCR. Power consumption: 60W. Dynamic range: 110dB (maximum 1kHz signal to A-weighted noise 20Hz–20kHz), 105dB (unweighted). Frequency response (sinewave 100mV input): 20Hz–20kHz ±0.5dB. THD (1V input, 1kHz): <0.05%. Wow & flutter: <l0.01% (unweighted), <0.006% (weighted RMS). Anti-aliasing filtration: –3dB at 37kHz. Sampling/bit rate: 644kHz. Maximum input/output levels: 24dBm. Mike preamp (optional): adds less than 1dB of noise for mikes between 100 and 1k impedance. Inputs: line 5k ohms, differential; edit audio 20k ohms, differential; mike 100k ohms, 6.8k ohms if phantom-powered (48V); video & sync 75 ohms. Outputs: line 47 ohms, single-ended, drives 600 ohms, switchable to balanced; edit audio 100 ohms, single-ended; headphones 150 ohms.
Dimensions: 19" W × 3" H × 11.5" D.
Source: long-term manufacturer's loan.
Price: $4600 plus $375 for mike preamplifiers (1987); no longer available (2021).
Manufacturer: dbx Inc., 71 Chapel St., Newton, MA 02195 (1987); dbx by HARMAN (2021). Web: dbxpro.com/en

COMPANY INFO
dbx Inc. (1987)
dbx by HARMAN (2021)
dbxpro.com/en
ARTICLE CONTENTS

COMMENTS
thethanimal's picture
Submitted by thethanimal on June 10, 2021 - 12:41pm

I really enjoyed the technical descriptions in this article; it’d be great if Stereophile could bring some of that technicality back in future articles. I haven’t thought about Coulombs in around 15 years so it was a nice mental workout. Not being an electrical engineer (but an engineer) I’m still catching up on the physics and theory of the hobby, but to my mind PDM sounds like it was a precursor to DSD. Any truth to that? Some technical history articles could be a good idea for a new column. (Unless some of that is already covered in print but not the website; I must confess to being a website-only reader.)

John Atkinson's picture
Submitted by John Atkinson on June 10, 2021 - 12:58pm
thethanimal wrote:
to my mind PDM sounds like it was a precursor to DSD. Any truth to that?

Yup (though there are differences in the details)

The dbx 700 was largely the work of the brilliant Robert Adams, who went on to design digital audio products for Analog Devices - see https://en.wikipedia.org/wiki/Bob_Adams_(electrical_engineer)

John Atkinson
Technical Editor, Stereophile

georgehifi's picture
Submitted by georgehifi on June 10, 2021 - 4:41pm

The Sony PCM F1 a couple of days ago, now the dbx 700, hopefully next the first mass retail CD player the Sony CDP-101 and 701 that I had both of and made my ears bleed!?!!Z
All this goes to show the youngsters of today what us older folk had to suffer through at the age of digital.
We all knew it had the potential, but my god we had to suffer for it with that early stuff. Hope you youngsters apricate it.!!!

Cheers George

cgh's picture
Submitted by cgh on June 11, 2021 - 7:26am

I agree with that comment: these old articles are really enjoyable... and comforting, like reading the back of classical music LPs, written during a time when writers didn't need to treat lay people like simple idiots.

I especially love the history, like Coulomb's story in that footnote. Reminds me of Faraday, who famously locked himself in a cage of his own making; or Gauss, who famously invented a "degaussing" device to help tame his wife's hair during the stormy and humid German spring time, only to accidentally kill her during an electrical storm.

Gordon Delgado's picture
Submitted by Gordon Delgado on December 14, 2021 - 5:32pm

This article takes me way back!
In the late 70s a company named Hybrid Systems (in Bedford, MA) made a set of A/D and D/A chips using a (then proprietary) "Delta Modulation With Memory".

These chips were used in the famous Audio/Pulse Model One, possibly the first hifi gear to use digital processing. In the Model One, it was used to create time delayed signals such as reverb for rear speakers (Quadraphonic!).

You can read all about it in Popular Electronics February 1979 here: https://www.google.ca/url?q=https://worldradiohistory.com/Archive-Poptronics/70s/1979/Poptronics-1979-02.pdf

Ever since that, I have wondered if delta modulation would make a well-deserved comeback. Still waiting, I guess...

--Gordo

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