Digital Signals

[benleeys]

I am always being told that digital signals are simply a string of 0s and 1s. So, as long as all the digits are there in the string, conversion to analog signals should produce identical sound irrespective of where the string is sourced from. Right?

So someone please tell me why I hear different quality of sound from different sources (like a CD played on different players) with digital signals converted by the same external DAC? Or is it my imagination?

 

[Rich]

So someone please tell me why I hear different quality of sound from different sources (like a CD played on different players) with digital signals converted by the same external DAC? Or is it my imagination?

Perhaps read errors; perhaps differences in jitter levels; perhaps someone with more knowledge than I can shed some light on this.

 

[amey01]

You can't apply logic/science to this.

Basically, 2008 science can't explain why you hear a difference. Simple as that.

The important thing is that you do hear a difference. So do I. As for the reason, maybe one day science will be able to explain it?

Just remember, not so long ago they thought the world was flat. In 10 years time we might be saying "when I was a kid we had no idea why digital signals sounded different".

 

[JonFo]

There are many reasons one CD player will sound different than another, all pretty explainable and objectively measurable.

A few off the top of my head are:

Unless feeding a digital bitstream to a processor, all CD players have Digital to analog converters followed by an analog section
- This is where, most commonly, the biggest differences are
- Analog section ‘tuning’ is common
- D/A specs and behavior also have audible (quite subtle, but real) differences

In the digital domain, there are several possible reasons there might be differences.
While the data is indeed pretty easy to propagate untouched, the timing of the samples into the D/A is critical. So once again, time-domain is important in Audio.
This is where Jitter comes in. If a digital system suffers from too high a jitter rate, the samples fed to the D/A will not resolve the original waveform. They might resolve the correct amplitude (data is data), but the points in time will be skewed, therefore resulting in audible differences.

Ina related item, read error correction and read stream buffering all contribute to ensuring ALL the samples are read correctly and time-sequenced out at the right rate with as high a level of integrity as possible.
Higher end players will use substantial read buffers and custom drive firmware (or firmware configs) to ensure they reduce read errors as far as possible. Meridian pioneered this back in the 80’s and 90’s.

I must point that in 2008, with all the good chipsets out there for both CD/DVD reading and D/A, there is no excuse for even modest cost players to have any issues with jitter and or D/A accuracy. 20 years of knowldge are baked into most modern chipsets.

So it really boils down (IMHO) to how well the analog portions are implemented and ‘voiced’ as to why one player sounds different than another.

 

[JonFo]

...

So someone please tell me why I hear different quality of sound from different sources (like a CD played on different players) with digital signals converted by the same external DAC? Or is it my imagination?

Ben,

One possible reason is the Clock synch between the transport and the D/A, as you are taking on the integration of two critical parts of the equation yourself.
This where timing errors (Jitter) can have an audible impact.

Also, if one of the transports has sub-par read error correction, or inaccurate buffering, that could also lead to differences.

I forget which megabuck player this was written about, but it had all the general concepts down, like a big read buffer. But their custom code that managed the buffer had a bug in that every time it wrapped (move back to filling front of buffer), it introduced a measurable delay in the output stream. That would skew the timing in the D/A’s and would be audible.

As I mentioned before, data is data, but the sequence and delay (time-domain items) are critical as well.

And BTW- the analog components of a system are also subject to time-domain errors. Just witness the phase havoc a passive crossover can impart on a signal, leading to time-domain errors between drivers.

 

[benleeys]

Ben,

One possible reason is the Clock synch between the transport and the D/A, as you are taking on the integration of two critical parts of the equation yourself.
This where timing errors (Jitter) can have an audible impact.

Also, if one of the transports has sub-par read error correction, or inaccurate buffering, that could also lead to differences.

I forget which megabuck player this was written about, but it had all the general concepts down, like a big read buffer. But their custom code that managed the buffer had a bug in that every time it wrapped (move back to filling front of buffer), it introduced a measurable delay in the output stream. That would skew the timing in the D/A’s and would be audible.

As I mentioned before, data is data, but the sequence and delay (time-domain items) are critical as well.

And BTW- the analog components of a system are also subject to time-domain errors. Just witness the phase havoc a passive crossover can impart on a signal, leading to time-domain errors between drivers.

Jon,

Am glad its not my imagination afterall. Thanks indeed. So it's basically the jitter bug.

Hopefully, in the not too distant future, if manufacturers use these good chipsets you mentioned earlier in their cheap players, we could all save tons of $ using these players as transports feeding a good video/audio processor like the Anthem D2 and not suffer the jitter bug. And people like Wadia will have to close shop.

 

[amey01]

Jon,

Am glad its not my imagination afterall. Thanks indeed. So it's basically the jitter bug.

Hopefully, in the not too distant future, if manufacturers use these good chipsets you mentioned earlier in their cheap players, we could all save tons of $ using these players as transports feeding a good video/audio processor like the Anthem D2 and not suffer the jitter bug. And people like Wadia will have to close shop.

Another way would be to choose a transport that allows master clock input, syncing it from the clock in the DAC.