How to best digitize an audio signal in a recording environment? (relevance of ADCs)

Question

I'm trying to build a decent recording environment for someone but this question is general. I am someone with more electronics knowledge than audio tech. Though by no means am I saying I am an expert in either.

I'm just trying to figure this out. I'm trying to find information but I just seem to hit a void on it. So I figured I'd ask here.

Say there is a case where you have a really nice good quality, low noise analogue signal. How do we best digitize this? What (tending towards best) systems are in place to turn the analogue signal to digital? Where do the bottlenecks occur?

Is it that beyond a basic ADC quality point (such as M-AUDIO fast track MKII), there isn't much relevance as to which ADC you use as much as which mic, room condition etc you use? What ADC systems do people use in studios? What exactly is in the mixer part (with many input lines)? Does that also have an ADC? Do studios normally have an ADC at the end of the stages? I see a lotta of info on high quality preamps and mixers etc. But I don't seem to find much on the final conversion to digital. Surely if you have an awesome signal, it will be of little effect if the final ADC is not good enough. No?

What am I missing? Is it that its quality of ADCs are so high that its just negligible when compared to the input mic, preamp etc? Or am I just looking at the wrong places? What is the industry best connections between an ADC and a computer? (plain old USB?) I am not asking about latency or any of the associated things, just purely about end quality.

I have an Behringer C1 condenser mic fed into an M-Audio Fast Track II box with Phantom Power and was wondering what were the next steps to improve quality. I built a preamp and I was wondering, how do I run it through the M-AUDIO without using its internal preamp as the only other way to digitize it would be to use the computers built-in "line in" input which is obviously poorer than a dedicated ADC. To be clear, this is not a "How can I make my recording environment better" question. I just want to understand where the bottlenecks exactly occur and hopefully gain some insight. I just provided details incase anyone was wondering where I'm coming from.

Answer 1

The leading manufacturers of ADCs are companies such as Apogee, Prism Sound, Lavry Engineering, and RME (to name just a few of the popular ones). All produce various white-papers and spec sheets showing the superiority of their designs.

But there is a serious debate as to what extent people can perceive quality differences between various ADCs.

Some claim to hear noticeable differences; but this can be contributed to the placebo effect, and pretty much none of these people have demonstrated this ability in a fair, blindfolded A/B test.

Empirical tests (some I have conducted myself) suggest that it is mainly cheap and old ADCs that can be distinguished from modern ADCs, whether expensive, moderately priced or even cheap ones. Interestingly, in some experiments people actually preferred the old and cheap ADCs, which is explained by the sound colouring these involve.

It is perhaps important to mention that even the cheapest ADCs nowadays are built with a technology (namely 1-bit delta-sigma conversion) that is far superior to the ADCs we had 20 years ago. This seems to marginalise audible differences.

What is important to mention is that most consumer products are not specialised ADCs. As such, the sound quality may be affected by various factors, such as relatively high noise levels or poor input/output stages.

I can say with certainty that a different room, mic choice or a mic-pre will yield far more audible sound differences than a different ADC.

What is the industry best connections between an ADC and a computer?

The connection itself has no effect on sound quality. Once digitised, the samples will be transferred onto the host machine perfectly, regardless the connection. From a functional perspective (not audio quality, but hardware issues), FireWire seemed to become the candidate of choice, providing higher performance than USB, but many manufacturers have experienced unreliable and inconsistent behaviour with FireWire connections (somewhat oddly, this applies to audio but not hard drive connections). So you'll find that many manufacturers now prefer USB connections over FireWire.

What ADC systems do people use in studios?

This is impossible to answer, but many professional studios use either Pro Tools HD interfaces or Apogee's. But many use other ADCs.

Do studios normally have an ADC at the end of the stages?

Normally the ADC, whether a dedicated one or part of a combo audio interface (with pre amps and monitor section), is connected directly to the DAW, allowing the connection of analogue signals to and from the DAW.

What exactly is in the mixer part (with many input lines)? Does that also have an ADC?

The role of the mixer is to accommodate inputs, outputs, and perform the mixing (summing), routing and processing of audio signals.

Some mixers are digital, meaning that analogue input signals are converted to digital straight after the input stage, then all processing/mixing/routing is done in the digital domain. The digital signals are then converted back to analogue before the analogue output stages. But there might also be digital outputs (ADAT/SPDIF) so the audio is just sent in its digital form.

Analog mixers perform all these tasks in the analog domain, so they don't involve ADCs.

Since it is common to connect analog mixers into a DAW (requiring a separate ADC), manufacturers like Mackie now offer analog desks that have an ADC build-in, and that can be connected to the DAW directly via USB or FireWire. They simply consolidate the ADC into the desk.

I built a preamp and I was wondering, how do I run it through the M-AUDIO without using its internal preamp

If your audio interface hasn't got a line-in input, you can't.

The computers built-in "line in" input which is obviously poorer than a dedicated ADC.

This may or may not be true. Some ADCs (like the ones on the Mac Pro) may not yield any audible difference compared to cheap dedicated ADCs or audio interfaces with ADCs. In fact, my Mac Pro line out connection has lower noise level than my Yamaha UR28M.