CD signal out vs transport interconnects. Why/which?

[roddo]

The more I read, the less I seem to know, if everyone's opinion is equally valid, and since you guys are never shy of an opinion...

I currently have an old DVD player I use to transport CD signal to a nice DAC. (SMSL RAW Pro DAC1) via coaxial. Sounds ok, but is starting to make squeaking sounds. I need to replace, but can I do better.

My DAC supports RCA, USB, TOSLINK, COAX, AES / EBU, and I2S inputs.

I'm going to try to summarize the various stats I've read here, on other forums, and wiki, and I'm hoping I can get a semi-scientific explanation that would justify maybe stepping up to a better CD player or transport. Please, no opinions without some kind of pseudo-science to back it up. Ive read to much of those already, and I'm still here searching!

CD signal is 16 bit / 44.1 kHz.

Coaxial transport is 24-bit/192kHz.

Optical is usually restricted to 20 bit / 48 kHz.

USB is 24-bit/96 kHz (or 192 khz for class 2)

AES / EBU is 24 bit / 48 khz (but possibly out to 32 bit / 96 or 192 khz.

I2s doesn't seem to have a cap, and uses some kind of wizard juice to transport data.

I'm wondering if I can go reasonably budget and grab something like a SMSL PL150 ($150) and connect via Coaxial.
Argument: Coaxial surpasses a CD's max resolution, so why go use a higher-res delivery?

Or,

Splash out for a SMSL PL200T, ($500) and connect via I2S or AES / EBU?
Argument: There is other stuff to consider like jitter and placebo effect, which these higher-end transports address.

Thanks!

 

[solderdude]

Look for posts from @NTTY

One should keep in mind that all I2s, AES/EBU, Toslink and SPDIF derives its clock speed from the transport.
Jitter reduction of the DAC in question is important.

 

[RandomEar]

All listed interfaces support the CD sample rate and bit depth. If fed with CD data, the interfaces will run at that data rate and bit depth (unless you find a CD transports which upsamples, which would be useless but also harmless) so their maximum capability is irrelevant.

@solderdude is right about clock and jitter. Nonetheless, I would generally recommend TOSLINK (optical) due to the inherent galvanic isolation. It will sound exactly the same as all the other interfaces, but you will never get ground loops.

 

[krabapple]

The more I read, the less I seem to know, if everyone's opinion is equally valid, and since you guys are never shy of an opinion...

Everyone's opinion is not equally valid.

Your 'old DVD player' is probably entirely adequate on its own as a DAC, i.e., no audible need for an outboard DAC.

The transport/lens components will likely fail before its DAC function. If it's making 'squeaking sounds' (can you give some more detail on that?) that's a sign of maybe needing lubrication...or worse to come.

Whatever you buy to replace it, is also likely entirely adequate as a DAC itself, without needing an outboard DAC.

But if you are wedded to the transport + DAC idea, Toslink is an excellent and inexpensive connector for transmitting CD (and DVD) rate two-channel data to a DAC.

 

[roddo]

Thanks for the quick replies.

Toslink appears to be a popular inexpensive connector.

What are the benefits of USB/i2s/aes besides the logistics of having other inputs?

Is, why do transports have so many connection options, if cheapo old optical is generally the best option for 16 bit \ 44.1?

 

[Vincent Kars]

Optical is usually restricted to 20 bit / 48 kHz.

In the 80's it was 16 bit / 48 kHz max. Today is is either 24/96 (the standard) but modern hardware can do better so 24/192 is doable.

USB is 24-bit/96 kHz (or 192 khz for class 2)

A DAC like the Topping D90 III does DSD 512 and 32 bit PCM 768 kHz. Basically the restriction is the bandwidth of USB in high speed mode.

 

[krabapple]

In the 80's it was 16 bit / 48 kHz max. Today is is either 24/96 (the standard) but modern hardware can do better so 24/192 is doable.


A DAC like the Topping D90 III does DSD 512 and 32 bit PCM 768 kHz. Basically the restriction is the bandwidth of USB in high speed mode.

The OP seems to be talking about CD playback. If so, those other formats and higher rates are superfluous.

 

[Casper]

why do transports have so many connection options, if cheapo old optical is generally the best option for 16 bit \ 44.1?

Historically, optical was for connecting consumer components and AES was a professional standard for things like DAT recorders digital mixers etc. Now it's still useful to have multiple output formats because you might already have another device (like a streamer) connected to your DAC's optical input so you can use the AES out of the transport to connect to the DAC and maybe later have your computer's USB connected so all of your sources run through your DAC.

 

[roddo]

Moving away from the connector, what about the player/transport?

As @solderdude alluded above, are there other factors that mess with the integrity of the data (like jitter) that are player related, which are addressed at the DAC end, if a more complex connection like usb\i2s can address?

I read stuff like i2s is the native internal format, and i2s out/HDMI/i2s into DAC path means (insert AMAZING audio expirence).

 

[solderdude]

I2S is intended for short communication lines between chips within a single device or even 2 boards.
It is easier to process internally because the signals are separated and thus can reach higher speeds (short PCB traces).
It has separate clock and data lines where SPDIF, Toslink, AES/EBU have the clock and data combined as a single signal which have to be separated again.
The advantage of a combined signal is that there is only 1 'line' where I2S requires 3 (or 4) lines (one for serial data and one 2 (or 3) for word and data clock) + ground.

I2S has the advantage that (because of the intended short lines) is that it is easier to reach high data rates.
There is no standard connection for I2S transport between devices as it was never intended for that goal.
It also requires proper impedance matching and making proper transmitters and receivers for that signal.

There also is no benefit for sound quality but when one does not want to use the handy USB connection and still want to reach very high speeds that can be reached using USB you can do that using I2S.
There is also HDMI which uses separate data + clock lines. (so only 2 lines + ground) and is designed for multiple formats
The clock of SPDIF, Toslink, AES/EBU can perfectly be recovered in any decent receiver with jitter rejection.
It is rather limited in bits/sample rates though... that's where USB (UAC2) comes in handy.

Of course, CD output is relatively low data rate 44.1/16 2ch so all of these data transport formats work well and there is NO benefit for I2S here.

 

[voodooless]

Just use SPDIF, either coax or optical. Has been working reliably for decades. Nothing changed to negate that fact.

 

[Mart68]

Is, why do transports have so many connection options, if cheapo old optical is generally the best option for 16 bit \ 44.1?

Manufacturers have to cater for the market, some won't buy a transport if it does not have AES or I2S since they have read that these connections have magical powers, and they believe it. No point losing a sale when it's not a massive bother or cost to implement all the options. Obviously it does add some to the cost of the device, maybe ten or twenty quid.

 

[roddo]

Thanks guys, all.

If using the player only as transport to dac across very short distance (stacked on top of each other), toslink or coaxial?

 

[popej]

DVD player should support 24/96 at analog output. Quite probably it already has DAC better than CD standard. Have you tried to use its analog output?
IMHO idea of CD transport plus DAC is a trick to make people buy more while getting more problems to solve, like jitter for example.

 

[Mart68]

IMHO idea of CD transport plus DAC is a trick to make people buy more while getting more problems to solve,

It was cheaper to buy the transport I have plus a DAC than to buy the CD player version of it, by a significant margin.

 

[voodooless]

toslink or coaxial?

Whichever cable you have lying around in your sock drawer…

 

[popej]

It was cheaper to buy the transport

What is this transport?

 

[Mart68]

What is this transport?

TEAC 701T - the CD player was an extra £500 over the transport.

 

[popej]

TEAC 701T - the CD player was an extra £500 over the transport.

I see. I tought I was responding to OP.

 

[Mart68]

I see. I tought I was responding to OP.

You made a general statement about transport plus DAC not being economical compared to a CD player, I was just pointing out that isn't always the case.

I agree with you that it's better on a technical level to have a CD player rather than DAC/transport, but not if it's going to cost more that way since the real world SQ difference is nil.