How are MDAC faders different from DCA faders?

[Ben B]

Title sums it up. Anyone know?

Thanks,
-Ben B

[JohnRoberts]

Originally Posted by Ben B

Title sums it up. Anyone know?

Thanks,
-Ben B

Well MDACs were (are?) D/A convertors where the digital word controlled the divider resistance string and you could also vary the analog reference voltage to effectively multiply the reference voltage by the digital code. I don't think these were ever that useful for audio gain manipulations, but the modern digital pots or digital rheostats are similar when configured so an audio input acts like a bipolar AC reference that can be attenuated by a digital code. While these are perhaps limited in step size resolution.

A DCA = Digital controlled amplifier? There are now Digitally controlled mic pres and line level stages that integrate digital pots onto IC with gain stages. I guess you could also convert a digital control word to control an analog VCA. Inside a digital console a DCA could be a simple as a line of software calling for a multiply.

I would ask whomever is using that terminology to explain what they mean.. they seem like old technology apples and new technology oranges. DCA may mean different things in different contexts (Dig controlled analog hardware vs, all digital domain hardware).

JR

[Ben B]

Originally Posted by JohnRoberts

Well MDACs were (are?) D/A convertors where the digital word controlled the divider resistance string and you could also vary the analog reference voltage to effectively multiply the reference voltage by the digital code. I don't think these were ever that useful for audio gain manipulations, but the modern digital pots or digital rheostats are similar when configured so an audio input acts like a bipolar AC reference that can be attenuated by a digital code. While these are perhaps limited in step size resolution.

A DCA = Digital controlled amplifier? There are now Digitally controlled mic pres and line level stages that integrate digital pots onto IC with gain stages. I guess you could also convert a digital control word to control an analog VCA. Inside a digital console a DCA could be a simple as a line of software calling for a multiply.

I would ask whomever is using that terminology to explain what they mean.. they seem like old technology apples and new technology oranges. DCA may mean different things in different contexts (Dig controlled analog hardware vs, all digital domain hardware).

JR

I'm speaking in terms of their implementation into console automation systems. The faders in the AWS 900, for example, are reportedly MDACs. I've seen DCA's (Digitally Controlled Attenuators/Digitally Controlled Amplifiers) utilized in older automation and fader grouping systems, such as some of the Yamaha live sound boards.

-Ben B

[Matt Syson]

Hi
There are crossover devices from MDAC to DCA (digitally controlled attenuators) and as John says, the term DCA could mean a variety of techniques from some relays with digital control varying gain or amplification (if in the feedback loop or not) to a D/A converter driving a VCA (voltage controlled amplifier).
I believe the MDAC was a 'digital' device in that it would scale in values 1,2,4,8,16 (etc) whereas devices such as Dallas DS1305(not sure of numbers!) use 'log' weighted resistor strings to have 'dB' or half dB steps.
I can think of several ways that Digital control of analogue audio could be done but it is down to the marketing department to highlight what is used in any given piece of gear.
Old desk designs used to have DC grouping before full 'automation' running against timecode for example.
Matt S