[PStamler]

Hi folks:

A lot of the early compressor-limiters used a feedback design (that it, the cobntrol voltage was derived from signals picked off after the gain control element: the Teletronics LA-2 and LA3, the UA 1176, etc. Feedforward compressors, as I understand it, didn't start to arrive until the 1960s and 1970s.

Why? Is there something about feedback compressors that makes them easier to design when part costs are limited? And were other early comp-limitters like the Federal, RCA and Fairchild also feedback?

Peace,
Paul

[Don Pearce[_3_]]

On Sun, 17 Feb 2019 10:30:41 -0800 (PST), PStamler
wrote:

Hi folks:

A lot of the early compressor-limiters used a feedback design (that it, the cobntrol voltage was derived from signals picked off after the gain control element: the Teletronics LA-2 and LA3, the UA 1176, etc. Feedforward compressors, as I understand it, didn't start to arrive until the 1960s and 1970s.

Why? Is there something about feedback compressors that makes them easier to design when part costs are limited? And were other early comp-limitters like the Federal, RCA and Fairchild also feedback?

Peace,
Paul

Feedback compressors need no processing power. A diode detector
feeding a gain-setting FET and you are done. Attack and release can be
set with variable resistors alongside capacitors. The circuit is
pretty trivial.

d

[[email protected]]

On Sunday, February 17, 2019 at 2:28:34 PM UTC-5, Don Pearce wrote:
On Sun, 17 Feb 2019 10:30:41 -0800 (PST), PStamler
wrote:

Hi folks:

A lot of the early compressor-limiters used a feedback design (that it, the cobntrol voltage was derived from signals picked off after the gain control element: the Teletronics LA-2 and LA3, the UA 1176, etc. Feedforward compressors, as I understand it, didn't start to arrive until the 1960s and 1970s.

Why? Is there something about feedback compressors that makes them easier to design when part costs are limited? And were other early comp-limitters like the Federal, RCA and Fairchild also feedback?

Peace,
Paul

Feedback compressors need no processing power. A diode detector
feeding a gain-setting FET and you are done. Attack and release can be
set with variable resistors alongside capacitors. The circuit is
pretty trivial.

d

an interesting question..

yes, it would be very difficult to build feed forward compressor with analog hardware because the accuracy of the detector and the VGA needs to be very high. It can be done in DSP. But I can't think of any advantage to using feed forward. The attack time is limited by the delay in the detector and filter, not by the propagation delay of the audio stages.


Are there any vintage analog hardware compressors that use feed forward?

mark

[Scott Dorsey]

PStamler wrote:
Hi folks:

A lot of the early compressor-limiters used a feedback design (that it, the=
cobntrol voltage was derived from signals picked off after the gain contro=
l element: the Teletronics LA-2 and LA3, the UA 1176, etc. Feedforward comp=
ressors, as I understand it, didn't start to arrive until the 1960s and 197=
0s.

Think of this as having feedback around the control path. If the gain on
the gain element drifts a lot, it will be compensated for. In the case of
incandescent lamp + cds cell elements, they drift an enormous amount.

The other nice thing is that it softens the knee of the compressor.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Robert Orban[_3_]]

In article ,
says...


Are there any vintage analog hardware compressors that use feed forward?

mark



The dbx compressors were feedforward. If I recall correctly, the dbx RMS
detector and VCA were temperature-compensated in such a way that they could
work together to get stable characteristics even when the environmental
temperature varied.

--Bob Orban