DAC Explanation

[Mike B]

So I am a bit confused by DAC (I know that they convert digital...) I have a collection of LP's, CD's and mp3's. Call it 100 LP's, 250 CD's, 2500 mp3's. I also listen to YouTube.

I know that the LP's need not pass through a DAC. The mp3's reside on my PC. If they come out the 3.5 mm jack I realize that the sound card has already converted digital to analog.

So if I play my CD's in a CD player they get converted to analog.

I think mp3's are mostly already degraded.

This leaves CD's with the output going from USB => DAC => amplification chain. But the CD's were recorded and then digitally written to the disk. Do modern CD players send the digital code from the CD directly to the DAC? I see different bit rates. But don't CD's have a built in bit rate? You can't make it better than original, can you?

And what if I play a song on YouTube or play a DVD or Bluetooth disk? Does an unconverted digital signal leave my USB and get converted in the DAC? Is the DAC "better" at converting?

Thank you

 

[RayDunzl]

Do modern CD players send the digital code from the CD directly to the DAC?

If your CD "player" has digital outputs - coaxial or optical S/PDIF - it can send the digits on the disc to an external DAC with those inputs.

That's what I do here.

Do modern CD players send the digital code from the CD directly to the DAC?

The data on a CD is encoded in a special way to be stored reliably on the CD. Those data bits are re-encoded into the S/PDIF format (or possibly an I2S interface) for transfer to the DAC, whether it is internal or external.

But don't CD's have a built in bit rate? You can't make it better than original, can you?

A Red Book CD is recorded at 44.1khz sample rate and a CD player with digital outputs sends at that rate to an external DAC.

If the CD data is being sent from a Computer with USB, the computer can change (resample) the data rate, if it is set to do so.

And what if I play a song on YouTube or play a DVD or Bluetooth disk? Does an unconverted digital signal leave my USB and get converted in the DAC?

The data in a USB connection is digital, with the music data fomatted for compatibility with USB Audio specifications.

The DAC (Digital to Analog Converter) will convert the digital data stream to analog for listening.

Is the DAC "better" at converting?

Some DACs are "better" than others when you measure their capabilities.

 

[RayDunzl]

In the end, all the digital encodings for music create a stream of numbers that represent the "voltage" of an analog waveforn sampled x times per second.

You could graph the digits and see the wave on paper.

The DAC takes in the numbers and produces a voltage wave.

A music "wave" looks like this:

Zoom way in to see the individual sample values.

16bit (CD) data has a range of +32767 to -32767

(edit: that's -32768, I forgot... signed binary values from 0111111111111111 to 1000000000000000)

The dots are 1/44100th second apart

A DAC typically converts that to a range of +/-2V and everything in between.

 

[garbulky]

So I am a bit confused by DAC (I know that they convert digital...) I have a collection of LP's, CD's and mp3's. Call it 100 LP's, 250 CD's, 2500 mp3's. I also listen to YouTube.

I know that the LP's need not pass through a DAC. The mp3's reside on my PC. If they come out the 3.5 mm jack I realize that the sound card has already converted digital to analog.

So if I play my CD's in a CD player they get converted to analog.

I think mp3's are mostly already degraded.

This leaves CD's with the output going from USB => DAC => amplification chain. But the CD's were recorded and then digitally written to the disk. Do modern CD players send the digital code from the CD directly to the DAC? I see different bit rates. But don't CD's have a built in bit rate? You can't make it better than original, can you?

And what if I play a song on YouTube or play a DVD or Bluetooth disk? Does an unconverted digital signal leave my USB and get converted in the DAC? Is the DAC "better" at converting?

Thank you

Yes. CD's "should" send the digita lcode from the CD directly to the DAC via USB. This is known as bit perfect. Now having said that , Windows somestimes resamples the digital sound. The CD sound samples at 441000 hz (44.1khz). Windows will sometimes resample it to 48khz. Here the sound is no longer bit perfect but a close approximation. To avoid this use a software player that supports WASAPI protocol. For instance Foobar does this (but it requires a plug in to donwload and configure). J-river also does it.

I don't think there is anything called a bluetooth disk. What are you referring to.

There are two types of audio playback - lossy and lossless. CD is lossless data. Blu Ray Dolby true HD is lossless data. It means it is an exact copy of what it was given digitally. Lossy data is mp3, internet video, streaming video, bluetooth audio (most occassions) and DVD (in most ocassions). Here the data is compressed and it loses information. That information cannot be recovered. In essence it is a poorer quality digital representation of the original.
So for instance for CD the bit rate is 14000 kilobits per second (kbps). That is lossless audio and it gives us a 16 bit signal at 44.1khz. An mp3 of this is typically about 128 kbps lossy audio. Bluetooth audio bitrate maxes out at 345 kbps but likely it's going to be much less about 192 or 256 kbps. DVD bitrate for dolby is about 192kbps for two channel audio.

Blu Ray audio is usually lossless has a pretty high bit rate = Dolby true HD can do multichannel up to 96khz at up to 18000 bits per second (though it rarely does this).

Is the dac better at converting? Well.... it depends on what you consider better? Your onboard soundcard on your computer is a DAC. The headphone jack on your old phone is a dac etc. Anything with a headphone jack has a dac onboard. What you probably mean is an external dac better? Measurably, the best external dacs can outperform standard onboard audio in terms of producing low distortion by quite a lot. Can you hear this difference, is something that you have to make your mind up about. Double blind testing shows that real world listening with nearly any audio device (though there is a very rare exception) is "supposed" to be indistinguishable from each other even though the onboard soundcard has higher distortion compared to the world's best DAC. Now is that REALLY the case? Do they all sound the same? Does a better performing dac sound better? That's up to you to decide.

 

[House de Kris]

Zoom way in to see the individual sample values.

16bit (CD) data has a range of +32767 to -32767

View attachment 87737

Real close. The coded numbers range from +32767 to -32768.

 

[Killingbeans]

Do modern CD players send the digital code from the CD directly to the DAC?

Yes, both modern and vintage CD players do that if they have digital outputs and you use them as a so-called 'transport'. Nothing has changed in that respect since the media was introduced.

I see different bit rates. But don't CD's have a built in bit rate?

The data on a redbook CD is 16bit/44.1kHz, but some players can do upsamling.

You can't make it better than original, can you?

Not in my opinion. Upsampling is a useful tool for the inner workings of a DAC(?), but for transportation of digital audio signals I don't really see the point. But honestly there are many users in here that have a better understanding of these things than me.

And what if I play a song on YouTube or play a DVD or Bluetooth disk? Does an unconverted digital signal leave my USB and get converted in the DAC?

Depends a lot on the media. There can be none or there can be a number of digital-to-digital conversions.

Is the DAC "better" at converting?

You mean if an external DAC is audibly superior to the one that's built into your CD player/PC/streamer/smartphone? Again, it depends. If the built in DAC is terrible, and the external one is not terrible, then yes. But quite often the built in DAC is perfectly fine, and in those cases the answer is 'no, not really'(IMO).

 

[Mike B]

I don't think there is anything called a bluetooth disk. What are you referring to.

My bad, I meant "Blu -ray"

 

[Asinus]

A CD will have a bitstream which the player assumes it will be 2ch sampled at 44.1kHz and each sample needs 16 bits. The actual DAC IC will typically need at least three inputs: data, bitclock and frameclock. The data input ideally will be the same stream read from the CD, the frameclock will be 44.1kHz and the bitclock is num_channels x num_bits x frameclock (1.4112MHz).

If somewhere along the path the clocks are changed the bitstream will most likely be modified, in some instances even if the nominal clock is the same the clock domain is different, so it could be resampled anyways to avoid glitches. If the player features tone controls or PEQ, it will could also be resampled to a higher bit-depth.

 

[magicscreen]

View attachment 87737

A DAC typically converts that to a range of +/-2V and everything in between.

But how will that points be converted to a continuous analog signal?
Is there a capacitor which will fill the signal between 2 points?

 

[BDWoody]

But how will that points be converted to a continuous analog signal?
Is there a capacitor which will fill the signal between 2 points?

That's the magic of sampling theory...it isn't intuitive, but it allows you to recreate the (band limited) sampled signal with no loss of information.

This video gets referenced a lot here, because it really explains it well. It's worth it to watch it a couple of times.

 

[RayDunzl]

But how will that points be converted to a continuous analog signal?
Is there a capacitor which will fill the signal between 2 points?

It is called the Reconstruction Filter.

 

[andreasmaaan]

I think mp3's are mostly already degraded.

It's absolutely true that MP3s are degraded in comparison to lossless digital audio (e.g. what's contained on a CD).

It's worth noting, though, that even medium-bitrate (e.g. 256kbps) MP3s have superior fidelity to any analogue medium. Not that there's any need these days, with ample storage space cheaply available, for even the slight loss of quality that lossy compression results in.

 

[UCrazyKid]

Watch this video. It will explain a lot in easily understood terms.

 

[andreasmaaan]

Watch this video. It will explain a lot in easily understood terms.

I haven't watched the whole video, but just be aware that in the first few minutes he propagates a common misconception about digital sampling, which makes me wonder whether the rest of his advice is worth taking...

 

[solderdude]

There is a lot of nonsense and the hand drawn illustrations are far from reality.
Watch Monty's video instead.