Audio DAC discussion

[6pack]

Seeing the general increase in people interested in wanting to know what a DAC (Digital-Analog Converter) is I have started this thread for more discussion from our inhouse audio experts.

Even I am a noob when it comes to audio and its related terminology. So sorry for any mistakes from my side.

What is DAC

In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or electric charge).

Most modern audio signals are stored in digital form (for example MP3s and CDs) and in order to be heard through speakers they must be converted into an analog signal. DACs are therefore found in CD players, digital music players, and PC sound cards.

Specialist standalone DACs can also be found in high-end hi-fi systems. These normally take the digital output of a CD player (or dedicated transport) and convert the signal into a line-level output that can then be fed into a pre-amplifier stage.

Similar digital-to-analog converters can be found in digital speakers such as USB speakers, and in sound cards.

Source: Wikipedia

Why use a DAC when the audio devices already have their own inbuilt dac?

Most CD players will only make a half-hearted effort at the Digital-to-Analog conversion process, relying on OEM converter chipsets and less than adequate amplification stages. These will usually share the same power supply as that of the CD mechanism, which itself is very demanding on power because of the constant feedback mechanisms involved in the read-back process.

Many audiophiles will go for a two-box alternative. The first box being a CD transport (or CD player being used as a transport) which, in turn, feeds into a DAC. The DAC then converts the digital signal into an analog one; producing the line-level output that can be fed into a pre-amplifier or integrated amplifier.

Most dedicated CD players will have a digital output on them as well as the analog output. If you connect the digital output of your CD player to a DAC then you will bypass the CD player's "internal DAC" (digital-to-analog portion of your CD player) and the external DAC will then be responsible for the conversion process.

This is an extremely effective way of upgrading a CD-based hi-fi system and can make an extreme impact on the quality of playback. Later, you can then consider whether or not to upgrade your CD player to a dedicated CD transport. It is even possible to use a computer as a transport by use of a USB interface between the computer and DAC (such an option exists for our DAC Kit 2.1 in the form of an internal add-on board) and appropriate software.

Source: Audio Note Kits - What is a DAC and how can my hi-fi benefit from having one?

Now that we know what a DAC is and why it is important if you want to hear good sound, lets get started with the discussions.

First, since I'm a complete noob in these matters, I would like to know how do I use for example a usb DAC correctly. What I know is that I will be using the usb output from computer to power the DAC. Where do I take the output from the comp to the DAC?

Let's take for ex. the NuForce uDAC on this page.

I believe a DAC is used as an alternative soundcard for the comp?

If so, how can I be sure that anything I hear from a cd does not go thru any transformation before it reaches this device? As I see there is no direct connection from the cd digital out to this device. If I have not connected the cd digital out to mainboard [strike](there is no such provision on my mobo for now)[/strike]*, will I get double converted audio? Then will it mean that the sound I hear will be less good than if the DAC was connected directly to the cd player?

* Edit: Oops! There is a spdif connection on the mobo, but there is no spdif output jack.

Another question is: I want the output of a DAC to come from computer speakers. Do the computer speakers we get have their own cheapo DAC's?

If yes then if a discrete DAC such as this is used, won't its good output be destroyed by the speakers DAC before being played on the speakers?

So then if that's the case what's the point in buying a discrete DAC?

 

[viralbug]

1) Your question is the answer. As you mentioned, the DAC is like an alternative sound card. In the case of a sound card, the audio signals from the CD will be sent to the sound card where it will be converted into analog signal and sent to your speakers/headphones.

With the USB DAC, the audio signal would be sent to the external DAC instead of your sound card. Again, digital to analog conversion takes place and sent to your speakers/headphones.

Basically, sound cards are internal DACs. But external DACs generally give a better sound because internal cards suffer from noise in power coming from PSU/motherboard.

From the page you quoted, I hope you get that by CD players they meant portable player and not your CD/DVD drive on PC. Your optical drive already transfers data digitally to your motherboard from where it is sent to sound card. Digital to analog conversion takes place only in the DAC (internal or external).

USB is just one way of transferring a digital signal. The same digital signal can be transferred by spdif coaxial or optical as well. The nuforce uDAC uses only the USB as input method. Likewise there are other DACs that use coaxial or optical for input.

2) Generally speakers do not have DACs and hence the need to feed them an analog signal.

But some higher end speakers do have internal DACs like the Z5500. To make use of the internal DAC of Z5500, you have to connect it with a digital interface, ie spdif.

If you are connecting your speakers via analog interface, that means the digital-analog conversion has already taken place and there's no digital signal to convert, so basically the speaker will just output the sound.

 

[Gannu]

2) Speakers do not have DACs and hence the need to feed them an analog signal.

Incorrect!

There are speakers which accept digital signals and have a DAC onboard. Eg. Z5500, Z680, Inspire 5.1 Digital.

If yes then if a discrete DAC such as this is used, won't its good output be destroyed by the speakers DAC before being played on the speakers?

Yes, if the DAC of the speakers is inferior compared to the one on the sound card/external DAC.

 

[viralbug]

^ yeah I was editing that part.

 

[6pack]

1) Your question is the answer. As you mentioned, the DAC is like an alternative sound card. In the case of a sound card, the audio signals from the CD will be sent to the sound card where it will be converted into analog signal and sent to your speakers/headphones.
With the USB DAC, the audio signal would be sent to the external DAC instead of your sound card. Again, digital to analog conversion takes place and sent to your speakers/headphones.
Basically, sound cards are internal DACs. But external DACs generally give a better sound because internal cards suffer from noise in power coming from PSU/motherboard.

correct me if i'm wrong. that audio signal coming out from cd drive is converted from digital to analog by cd drive itself right? so basically the external DAc will get a polluted source to convert (if the term is right).

From the page you quoted, I hope you get that by CD players they meant portable player and not your CD/DVD drive on PC. Your optical drive already transfers data digitally to your motherboard from where it is sent to sound card. Digital to analog conversion takes place only in the DAC (internal or external).

USB is just one way of transferring a digital signal. The same digital signal can be transferred by spdif coaxial or optical as well. The nuforce uDAC uses only the USB as input method. Likewise there are other DACs that use coaxial or optical for input.

2) Generally speakers do not have DACs and hence the need to feed them an analog signal.
But some higher end speakers do have internal DACs like the Z5500. To make use of the internal DAC of Z5500, you have to connect it with a digital interface, ie spdif.
If you are connecting your speakers via analog interface, that means the digital-analog conversion has already taken place and there's no digital signal to convert, so basically the speaker will just output the sound.

What if my pc cd player is not connected to a digital input on board? I mean just the 40 pin ide cable is connected. Then will it output digital sound?
Right now I only have an onboard audio and use the headphone jack (or the rca jack at back - speakers) to listen to music. So this means i'm currently hearing sound from onboard dac. So how will the Nuforce uDac help me to get better sound if i connect its input to my comp headphone output which must have got some audio loss from onboard dac (if its inferior)?

 

[Aces170]

Right now I only have an onboard audio and use the headphone jack (or the rca jack at back - speakers) to listen to music. So this means i'm currently hearing sound from onboard dac. So how will the Nuforce uDac help me to get better sound if i connect its input to my comp headphone output which must have got some audio loss from onboard dac (if its inferior)?

By onboard, it doesn't mean the motherboard's sound chipset, but a DAC on the CD drive itself (I am unsure of this, there might be digital to analog conversion in the headphones itself), as you can listen to CD music even without logging onto Windows in quite a few systems.

 

[Gannu]

correct me if i'm wrong. that audio signal coming out from cd drive is converted from digital to analog by cd drive itself right? so basically the external DAc will get a polluted source to convert (if the term is right).

No, don't think it happens that way. The optical drive sends the signal in the form of digital output - 0s and 1s so long as it reaches the audio chip on the motherboard which decodes it as an analog output. If the board has a digital-out like the optical or coaxial out, it sends the same untouched signal to the external DAC of the AVR or the speakers.

What if my pc cd player is not connected to a digital input on board? I mean just the 40 pin ide cable is connected. Then will it output digital sound?

I'm not sure of the IDE interface but AFAIR the earlier optical drives did come with a separate header intended to be connected to the sound card/motherboard. I will let someone else answer this query.

Right now I only have an onboard audio and use the headphone jack (or the rca jack at back - speakers) to listen to music. So this means i'm currently hearing sound from onboard dac. So how will the Nuforce uDac help me to get better sound if i connect its input to my comp headphone output which must have got some audio loss from onboard dac (if its inferior)?

The uDAC accepts the input through USB which still is the digital input. Which means the signal is bypassed from your motherboard audio-chip. The decoding happens inside the uDAC's DAC and the analog output though the RCA/headphones. The DAC inside the uDAC is far superior to that of the onboard audio chip of your motherboard (or any motherboard for that matter!) which means you'll get a better sound from this DAC over your motherboard 3.5mm outs.

 

[6pack]

Let me clear my confused mind. According to me when listening to an audio cd from pc cd drive (if i do not connect the cd digital out to board digital in) then:

CD (DAC) -> onboard sound (DAC) -> headphones?

I don't see any other way the sound can come unaltered from cd if I have not connected a cable to the cd digital out to bypass the cd drives DAC.

So if I use Nuforce DAC, then it becomes:

CD (DAC) -> NuForce (DAC) via usb??

 

[viralbug]

I'm not sure of the IDE interface but AFAIR the earlier optical drives did come with a separate header intended to be connected to the sound card/motherboard. I will let someone else answer this query.

Yes the IDE drives did come with an additional audio connector. Earlier it was necessary to connect it to the motherboard/sound card for listening to an audio cd. However, this wasn't necessary later on. There was an option in control panel and media players to enable digital cd playback. With this enabled there is no need to connect the audio connector as the sound is then transferred digitally to the motherboard via IDE. Now every media player can play an audio cd without the need of connecting the cd drive to sound card.

SATA drives don't have this audio connector.

Let me clear my confused mind. According to me when listening to an audio cd from pc cd drive (if i do not connect the cd digital out to board digital in) then:

CD (DAC) -> onboard sound (DAC) -> headphones?

I don't see any other way the sound can come unaltered from cd if I have not connected a cable to the cd digital out to bypass the cd drives DAC.

So if I use Nuforce DAC, then it becomes:

CD (DAC) -> NuForce (DAC) via usb??

The cd drive does NOT have a DAC. So the the sound is digitally sent to the motherboard. Right now, this is how it is:

CD -> Motherboard interface -> Onboard sound (Here the digital sound is converted to analog via DAC) -> headphones

With the nuforce DAC

CD -> Motherboard interface -> nuforce DAC via USB (Here the digital sound is converted to analog via DAC)) -> headphones

Basically, you are using the nuforce DAC instead of the onboard DAC, which is far better in terms of quality than the onboard DAC and hence you get better sound quality

In simpler terms, you can view the external nuforce DAC as an external sound card. Instead of using a PCI interface for an internal sound card, you are using USB interface since its an external.

 

[Gannu]

@6pack: Do you has an IDE or a SATA optical drive?

 

[Aces170]

@ Gannu, 6Pack, and Viralbug

I distinctly remember listening to audio CD's without booting Windows way back in 2000. So I think the CD drive itself has a DAC.

 

[6pack]

@6pack: Do you has an IDE or a SATA optical drive?

IDE drive. I tried as much as I could, but I could not find the enable digital cd playback that @viralbug was talking of in windows 7. But I do remember it was there in XP. :S

@Aces, you are right. My old creative cd rom drive had option of audio out jack in it and I remember playing audios in it in dos mode. My current dvd drive does not have an audio out though.

 

[Gannu]

@ Gannu, 6Pack, and Viralbug
I distinctly remember listening to audio CD's without booting Windows way back in 2000. So I think the CD drive itself has a DAC.

Like I said before Aces, I'm not sure about IDE interfaces. I do remember these drives sported a 3.5mm jack but I had no luck back then using the jack to drive my earphones.

 

[Aces170]

^^ Oh is it, I haven't really used that feature in recent times...

 

[viralbug]

@ Gannu, 6Pack, and Viralbug

I distinctly remember listening to audio CD's without booting Windows way back in 2000. So I think the CD drive itself has a DAC.

AFAIK, although it wasn't a complete boot, it was sort of a partial boot where the BIOS would power only the devices required to play the audio CD. The BIOS included a set of instructions for the decoding process in the audio chip as well. It would power up the cd drive and keyboard so you could use buttons on keyboard to play/pause/forward etc.

As far as audio not being able to play via the headphone jack on cd drive, I guess it must be because the audio connector on cd drive might not be connected to the sound card.

IDE drive. I tried as much as I could, but I could not find the enable digital cd playback that @viralbug was talking of in windows 7. But I do remember it was there in XP. :S

@Aces, you are right. My old creative cd rom drive had option of audio out jack in it and I remember playing audios in it in dos mode. My current dvd drive does not have an audio out though.

As I said, it was generally found in earlier times. I'm not sure if the option is still found in the current OS/players. I'm sure it is automatically enabled since we don't connect anything between the optical drive and sound card. IDE/SATA is the only interface through which the optical drive is connected.

 

[6pack]

^ but there is an option in the drives to connect digital out cable to sound card. That means a cd drive must be doing some processing of it own on the signals right?

Edit: Where to get something like shown in fig 10 or fig 12 in this link

 

[cranky]

As said, a CD-ROM and other disc playback device will have an onboard DAC if it has an analogue connector at the back. In recent OS'es WMP can recognise and control audio CDS over the IDE/SATA interface so no DAC is required, though some manufacturers may keep it for legacy reasons and for the fact that a PCB revision may actually cost more money than removing the DAC/connectors. An easy way to find out is to look at the back of the drive, if it has connector, it has a DAC.

It is assumed that till the point the digital conversion takes place (enters your DAC) it is bit-perfect. It is not a perfect assumption, but it will have to do.

Sometimes, CD-ROMs will also have a digital output connector. This supplies a signal identical to SPDIF except for level, and some interface circuitry may be required to mate it to a suitable DAC.

When you connect a USB DAC, it does not transfer digital in the same way as coaxial or optical. The data is sent in a very separate container, and is electrically different from the SPDIF interface. For USB 1.1 compatible DACs, no drivers are necessary as the protocols are built into the specification. windows will recognise and install the drivers for such devices automatically, and they will appear as a new device in sound manager. USB 2.0 DACs will need dedicated drivers, and they operate in what is known as async USB mode, so they are much less prone to jitter and dropouts as is the case with USB 1.1 DACs.

When you use the word DAC, be aware that it means different things. A DAC is a chip, a part of a chip, and a complete box with a variety of connections and input/output configurations. It is something like the word 'engine', which could mean various things depending on the context. This causes much confusion.

 

[Gannu]

Edit: Where to get something like shown in fig 10 or fig 12 in this link

No clue but you can make one for the SPDIF coaxial with the guide sangram has made, provided your motherboard has an onboard SPDIF header!

Btw does your speakers accept coaxial or optical input? Or do you have an AVR? Or a DAC that accepts coaxial/optical inputs? With only these, can you use the digital outputs mentioned in figures 10 & 12!

 

[viralbug]

Connecting a digital out cable to sound card would make the sound card to do all the processing.

I'm a bit confused now, it seems there are analog out connectors from cd drives as well. For audio CD's, the cd drive works as a standalone cd player. So here I suppose there has to be some kind of a DAC. :S

 

[Gannu]

@ Gannu, 6Pack, and Viralbug
I distinctly remember listening to audio CD's without booting Windows way back in 2000. So I think the CD drive itself has a DAC.

BTW Aces was right!

This is what the link 6pack posted had to say:

It goes like this: when an audio CD is inserted in a CD-ROM drive, this drive has to convert data, read in digital format, into an analogue audio signal, seeing that sound is an analogue signal. This analogue signal is then sent to the sound card via a suitable cable. For people that care for the signal's noise level, there are two points here that can lower the quality of audio. In the first place, the CD-ROM drive can use a poor quality D/A (digital-analogue) converter and so generate noise. In second place, seeing that transmission between the CD-ROM drive and the sound card is carried out in analogue format, the cable used for connecting may pick up noise from electromagnetic interference inside the computer.