Question for an EE

[myinitialsaredac]

How does a dac work?
 
No really, I mean does it function essentially like a summing operational amplifier?
 
If yes, would it be the number of voltage inputs into the operational amplifier that affect its bit depth?
 
If yes to the above question then doesn't the additional 8 voltage inputs for 24bit have equal weight (assuming the resistors are the same value) in the final summation? 
 
Again if yes to the above, wouldn't that make 24 bit audio much higher resolution than 16 bit?
 
If no to any of the above please explain and feel free to skip the next questions. 
 
Thanks in advance. 
 
Dave

 

[brconner]

Yes a DAC essentially operates like a summing amplifier. Each bit is not the same value. A 16 bit DAC can output 2^16 = 65536 different voltages while a 24 bit DAC can output 2 ^ 24 = 16777216 different voltages. So the 24 bit DAC is a significantly higher resolution than the 16 bit. 
 
The way this works is just like binary. The first bit has some voltage value, the second bit is twice the voltage of the first bit, the third bit is twice as large as the second bit and this continues to however many bits there are in the system. Its works like binary. 

 

[myinitialsaredac]

Quote:

Yes a DAC essentially operates like a summing amplifier. Each bit is not the same value. A 16 bit DAC can output 2^16 = 65536 different voltages while a 24 bit DAC can output 2 ^ 24 = 16777216 different voltages. So the 24 bit DAC is a significantly higher resolution than the 16 bit. 
 
The way this works is just like binary. The first bit has some voltage value, the second bit is twice the voltage of the first bit, the third bit is twice as large as the second bit and this continues to however many bits there are in the system. Its works like binary. 

I see, so are the resistors increasing in each step?
 
I guess my question is why are all of the inputs not unity?
 
Thanks for the input,
Dave

 

[ramicio]

There is much more to a DAC than just a binary to voltage converter.  From what I understand there is trigonometry involved and they oversample by A LOT and do a lot of math to smooth out the signal to get as close to analog as possible.  But a DAC is really a wide range of things.  An audio DAC is its own subgroup of a DAC.

 

[brconner]

 

A DAC doesn't operate with analog input voltages. A digital command is sent (serially or in parallel) to a DAC and the DAC outputs an analog signal. Digital to analog converter. The way it converts the digital command to an analog signal can be done in several ways. The wikipedia page gives a pretty decent explanation of what the binary value means and mentions some of the different methods used to convert the digital command to analog.
 
http://en.wikipedia.org/wiki/Digital-to-analog_converter 
 

Quote:

There is much more to a DAC than just a binary to voltage converter.  From what I understand there is trigonometry involved and they oversample by A LOT and do a lot of math to smooth out the signal to get as close to analog as possible.  But a DAC is really a wide range of things.  An audio DAC is its own subgroup of a DAC.

In its most basic form thats all a DAC is. DACs have come a long way since they've been invented and now have the features you're talking about and others as well. Most signals are smoothed out just using a low-pass filter though. Some DACs use a sigma-delta converter which are more complicated than say an R-2R design. Just depends on what application your doing to determine the type of DAC you want.
 
 
 

 

[ramicio]

Yes, sigma-delta is what I was referring to.  Something that just turns a digital number into an analog signal with no mathematics will sound like an 8-bit Nintendo system.  It's obvious you can synthesize sounds, but you can't play actual lifelike audio over DACs like that.

 

[myinitialsaredac]

@brconner

Aren't digital commands voltage signals? 
 
@ramicio
 
I am actually asking more because I was confused by a post about dacs of higher bitrate adding only headroom, while it seems that if they operate as summing opamps that would not be the case...
 
 
Dave
 

 

[brconner]

Yes they are voltage signals, but they're digital signals. Here's a good explanation on em.
 
http://en.wikipedia.org/wiki/Digital_signal
 

 

[Iniamyen]

Quote:

Yes they are voltage signals, but they're digital signals. Here's a good explanation on em.
 
http://en.wikipedia.org/wiki/Digital_signal
 

A voltage is a voltage; there's nothing special about the digital-level voltages except how they are interpreted. It becomes "digital" when we abstract it and call it as such. The simple R-2R resistive ladder DAC doesn't care if it gets 5V or 4V; it will do the same thing to the signals on its inputs. In this way, this DAC is entirely an analog device but it only makes sense to drive it with signals that have a "digital meaning" to us.