Newbie question on Computer->DAC Setup

[wgcho]

Hi everyone,

 

I consider myself quite technical (advanced degree in Computer Science) but as I am relatively new to digital music, I am having these burning questions - which seem quite basic, but hard to find answer for.

 

- I have a Mac Mini connected to Lindeman DAC via USB. I thought, in this way, the music file (AFLAC) is directly passed to the DAC, and therefore as long as the cable is good enough to not cause jitter, the sound quality should NOT depend on the music player I am using. I currently use iTunes, but people say I will get better sound by using something like Amarra. If this is true, that means some sort of signal processing is happening at the software level. Can I set it up so that the raw digital music is sent to the DAC so all the audio processing happens independently of the computer or software?

 

- Similar question, in this case for when I am using an iPod transport. I was reading a review for the Wadia 171 transport in which it says the audio quality was different when connecting an iPod vs. an iPad. The reviewer noted that the difference could be coming from the iPad cable. How is this possible? Does the iPod/iPad transport do more than extracting digital music and sending it over to the DAC? How can a longer cable for digital transport affect the audio quality??

 

Although these two are different questions, they are actually the same in the sense that I am asking for what happens in the source-to-DAC process.

 

This is probably a very fundamental question, so any pointers to a good reading is also welcome!

[ringenesherre]

Ok, that's actually more than two questions. Here are my answers:

 

1) iTunes is bit-perfect if you run at 100 volume (slider in iTunes), adjust the sample rate in the Midi settings (outside iTunes), deactivate "Sound enhancer", equalization, cross fade playback, and sound check. Differences between e.g. Amarra and iTunes could then be due to Amarra changing the signal or computer load and thereby noise affecting the playback (very unlikely from my perspective given that the Lindeman has a decent asynchronous USB interface).

 

2) Programs like Pure Music, Decibel, Audirvana etc. can provide value nevertheless. They can automatically adjust the sample rate or resample using better SRC implementations etc. Personally, I am fine with bit-perfect iTunes as almost all my music is 16/44.1 anyway.

 

3) Claims regarding different quality of going digitally out of iPod / iPad I would not believe, in particular if the DAC attached to the digital dock has a decent jitter rejection. I have not tried the Wadia, but with the Cambridge Audio id100, there is no difference between my iPhone 3GS and iPad 3rd generation.

 

4) Usually, in the source-to-DAC process, audio data is streamed via USB, optical or coaxial digital cables. Thus, in theory different loads of the computer, cables, and a lot of other hings can introduce jitter (samples arriving a little bit too early or too late). With asynchronous USB, the stream is clocked in the converter, i.e., previous jitter should not matter. Most decent DACs nowadays reject jitter very well (including your Lindeman). So don't worry too much about.

 

5) There are people who will want to tell you that two identical music files ripped from the same CD using different cd drives / ripping software / cables will sound systematically different on playback. That is, as you will understand with your background, impossible if the two files are bit-by-bit identical. You will also hear laughable concepts like "digital generations", i.e., that sound quality degrades with each copy of the file from one place to another. Most of these ridiculous ideas come from the analog world, where audiophiles are used to care about quality of the turntable cartridge, generations on analog tape etc.

 

Cheers,

Peter

[ringenesherre]

Question on the iTunes player:

 

I understand that turning off equalizer in iTunes is needed for bit-perfect. But what about turning it on, keep the frequencies untouched and lower the amp setting in the equalizer to below medium? (medium is default setting). Would this hurt SQ? anyone

 

The reason why I'm asking this is that the default setting (Equalizer turned off) seems loud.

 

 

thanks

 

If you ask me, I would say probably not much. The stream will be changed (so no bit-perfect), though. Why not use the volume control?

 

Cheers,

Peter

[wgcho]

Peter, thank you so much for your detailed answer. It's good to know my engineering mind was not too far off. At the same time, it is quite mind boggling how much BS is going on in various forums, reviews and offline shops. I'm actually quite surprised these false information are not being corrected. Someone should perhaps summarize all the truths and myths about digital music, once and for all.

 

Once again, thank you!