Quality aspects of ADC, Does quality gear makes a difference? Options

[ktf]

Hi all!

Background information (safe to skip )
Currently I'm preparing a large archival operation: my musical society has a collection of recordings on compact cassettes from 1980 to 1990, about 140, which I think have to be digitalized to protect them from deteriorating. I have found a nice tape deck (Nakamichi DR-3) but it has to stay at the office of the executive committee. A friend of mine has a nice ADC for this job, a quality portable mixing console with USB out, but it cannot stay at the office as it is more or less public and he doesn't trust everyone there. However, it is too much hassle to bring it every time, as I think this operation will cost about a year: 3 recordings a week. So, I guess I'm stuck with my own ADC: a Creative X-Fi Surround 5.1 USB-card, which is not really made for the job, but I can at least leave it at the office, as it isn't that valuable.

On-topic
That friend of mine that offered me his portable mixing-console with ADC argued that with a cheap ADC all little nuances and details would vanish, so I should look for another solution than using my Creative ADC. That made me think: i'm much more a theoretician than he is, so I was wondering, what makes a high quality ADC? I know the working principle of several ADCs, I can't imagine which link in the chain would be capable of 'erasing details' anyway. How does a non-linearity in an ADC sounds like in practice? And jitter? I guess uncorrelated, random jitter could sound like 'more noise', as it is random. To me it seems a low-quality ADC doesn't add anything but noise and a non-linearity, let alone it could remove things from the signal.

In short: what could a low-quality ADC do with the signal except adding noise? Probably I'm far too short sighted, can anyone enlighten me?

[DVDdoug]

So, the THD+N (for distortion and non-linearity) and SNR are the only specifications that matter for an ADC?

With any audio equipment there are 3 sound-quality specs/factors that concern me.*
1. Noise
2. Distortion
3. Frequency Response

Ethan Winer adds "time-based errors" (and room acoustics). But as I said, I've never had any time-based issues with properly-working equipment. In a "scientific" discussion time-bases issues must be included because you can obviously muck-up the sound by changing/varying the playback speed, or the clock in a digital system.

And with modern electronics, noise is the only defect I ever hear. It's easy to get low distortion (below the threshold of human detectability) and flat frequency response, although if you want to get "ruler flat" frequency response beyond 20kHz from a real-world DAC or ADC, you might need to go to a higher sample rate (higher than 44.1 or 48kHz).

With transducers (speakers, headphones, and microphones), frequency response becomes a BIG deal!


* I guess I should say power (watts) is a major spec that I consider when it comes to power amps, and of course there are other features & functions to consider that don't directly relate directlyto sound quality.

[ktf]

With any audio equipment there are 3 sound-quality specs/factors that concern me.*

Well, I could name another important one for speakers: their radiation patern. For some speakers, there's quite a difference between sitting exactly in front of it or at an angle of about 10 degrees, for some speakers, this difference is only slight. Like you probably overlooked this, I started this topic to see whether I overlooked something on considering ADCs too. When I posted this topic, I was concerned about DAC-slew for example, as would occur in sample-and-hold DACs, and something similar in ADCs. You can think of so much things that can go wrong like improper shielding, aliasing, channel crosstalk, but I guess these can all be measured under those two measures: THD+N and SNR.

However, to really convince myself, I just did some tests: play some music with a high dynamic range on the soundcard and record it through line-in (direct loopback), play that recording and record it, and so on. I 'stacked' the effect of DAC and ADC in this way 12 times, and I really can't hear a difference, so I'm really confident now that my ADC can do the job It also revealed the soundcard of my laptop is really, really badly build: when I plug-in my USB-soundcard it start to hum at quite high levels, (-50dB or something similar) not really you would expect of a laptop that is priced over 3000 dollar (luckily I got it for much less) but I guess sound isn't a priority on those things.

This post has been edited by ktf: Mar 4 2011, 23:43