¿What is really a DCA?

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JAY X

Well-known member
Joined
Jan 9, 2009
Messages
683
Hi All!

Latelly i have heard this thre letters quite often: DCA. Ok, it stands for Digitally controlled amplifier, but it does not seem to refer to a particular device or model of chip.

it could be a VCA controlled by a DAC or  a digital chip like the ti pga2310... but maybe it is more than these two examples.

If anyone can put abit more light on this concept, is wellcome!

Thanks  a lot!

JAy X
 
I suspect DCA is used as a general concept similar to VCA grouping in analog consoles where digital control signals are grouped or manipulated. Inside digital consoles there are not specific circuits changing the gain, just multiplications performed inside digital processors.

There are several different variants of digital gain control for analog circuit blocks.

JR
 
JAY X said:
Hi All!

Latelly i have heard this thre letters quite often: DCA. Ok, it stands for Digitally controlled amplifier, but it does not seem to refer to a particular device or model of chip.

In the world of live sound mixing consoles, "DCA" is misused in the same way as "VCA." By this I mean: the faders on a console labeled "VCA" or "DCA" should be called "VCA group master" or "DCA group master." 

Why?

In an analog console with VCAs, the channel fader does not pass audio. Instead, it sets, based on channel fader position, a control voltage for the voltage-controlled amplifier through which the channel audio passes. It is the control voltage which determines channel level.

Now all VCA consoles have the concept of VCA grouping. A VCA group fader controls the level of all channels assigned to that group. Each VCA group fader outputs a control voltage relative to fader position. In each channel, the channel fader control voltage is added to the group control voltage to determine the actual VCA gain setting. The ultimate effect is that moving a group fader is exactly like moving the channel fader. (This is different from audio subgrouping, where the channels feeding the group are summed and then the group fader affects the final level of that group. From a mix perspective, the real difference is that a VCA group fader move affects post-channel-fader aux senses whereas a subgroup fader move does not.)

The "DCA" concept is analogous (sorry for the pun). It should be obvious that on a digital console the channel fader, like on the VCA console, does not directly manipulate the channel's audio level. Instead it outputs a position-dependent number which represents intended gain. The DCA group fader does the same thing, generating a position-dependent gain-set number. For each channel, the processing determines actual gain by considering the channel position number as well as the position number of all assigned groups, and comes up with a final scale factor.

So, calling the faders "DCAs" is correct in the sense that they are "digital controls" and the "amplifier" is a multiplier in some processing pipeline. But they should still be called "DCA Group" faders.

sorry for the length. coffee good.
 
Hi all!

Thanks a lot for the explanations. Now is clear!

As always, some call amplifier what really is a line of code in a dsp chip...

Jay x
 
JAY X said:
Hi All!

Latelly i have heard this thre letters quite often: DCA. Ok, it stands for Digitally controlled amplifier, but it does not seem to refer to a particular device or model of chip.

it could be a VCA controlled by a DAC or  a digital chip like the ti pga2310... but maybe it is more than these two examples.

If anyone can put abit more light on this concept, is wellcome!

Thanks  a lot!

JAy X
In the analog mixers world, DCA had a specific meaning, at a time when it could be considered as a viable proposition, but it was always a building block, not a single component, generally an opamp mated with a digitally controlled-element that could be an analog MUX combined with a string of resistors or an MDAC
http://www.analog.com/library/analogdialogue/archives/44-09/mdac.html
This went out of fashion at the end of the 90's because of the cost and the zipper noise, whilst digital audio provided more interesting features for less money.
Today, some applications take advantage of digital potentiometers.
https://www.maximintegrated.com/en/products/analog/data-converters/digital-potentiometers/application-ideas.html
 
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