High-Level Questions about ADC, DAC, CODECs, and Hi-End Audio Interfaces

Thread Starter

Dolmetscher007

Joined Mar 21, 2019
29
I am really into audio engineering and digital home recording. I find the products in that space are full of marketing double-speak, exaggerated claims, and meaningless adjectives like... "warm, buttery, harsh, squishy, chewy, gluey... etc." I was wondering if you guys could help answer a couple of questions for me without slant or auditory opinion; just details and data.

ADCs
Analog-to-Digital Converters, as far as I know, do one thing. They sample an incoming signal at a specific rate, typically 44.1 kHz - 196 kHz. And they encode those samples as binary "words," typically at 24-bit. When recording digital audio, ADCs appear in a piece of gear called an "Audio Interface," which you connect to a computer using, USB, Firewire, Thunderbolt, etc. The data from the ADC is passed into the computer for storage and manipulation using specific software called a DAW (Digital Audio Workstation).

Question 1: Are there any differences between one ADC over another? Obviously there can be reliability or performance issues that make Company A's ADCs "better" than Company B's. And I am sure that there are ADC for all types of applications other than just recording audio for entertainment. I'm sure there are hundreds it not thousands of applications for ADC, military, automotive, cellular technologies, etc etc. But, when it comes to ADCs used for digital audio... it seems to me like the industry would kind of, as a whole, figure out which company makes the "best" ADC for pro audio, and everyone would just use that one.

Question 2: Audio interfaces on the market have wildly varying retail prices. They start as low as ~$69 and go up past >$10,000. There are a lot of aspects and features other than just ADC that affect the final price. For example, pre-amps. In order to record a descent sounding audio signal, it must first go through a pre-amp to boost it to a higher level. An audio interfaces pre-amp(s) probably impact its price the most. However, if you are a true professional audio engineer, it is highly unlikely that you would be using the preamps that come stock in your audio interface. The world's highest quality audio pre-amps, are stand-alone rack-mounted modules or are in a massive console.

If I wanted to build an audio interface that had no pre-amps, no features, no nothing, other than simple "The world's highest quality analog to digital converters" would that still be a complex project that would require electrical engineers working for years to come up with a design, or... could I just call up Texas Instruments and ask them for their best ADC and some documentation on how to incorporate it into a circuit. Then just solder it to a PCB along with whatever power management circuit it requires, and send its output through whatever interface chipset (Thunderbolt, or whatever) is considered "the best" these days? And that's it?

The reason I ask is... I own some really great analog pre-amps that were very expensive, and sound fantastic. I need a new audio interface, but as I am looking at what is on the market right now, they are so massively expensive, and I hate to spend north of $1k on a piece of equipment that is nothing more than a box that holds 10-15 ADCs that all cost <$5 ea. and sends it to my computer along ~$20 of additional chips and passive components. Am I over-simplifying things in my head?
 

crutschow

Joined Mar 14, 2008
25,417
Question 1: Yes there are some differences that affect audio performance mainly signal/noise ratio and distortion.

Question 2: I would say some of the difference in price is hype.
Again I would say that S/N ratio and distortion are the two most important parameters.

Look for A/D converters specifically designed for audio use as they are optimized for that purpose.
 

nsaspook

Joined Aug 27, 2009
7,588
Electronics are almost never the limiting factor in high-end audio reproduction. Speakers, speaker placement and room acoustics are what separates the good from the best in sound. Spend your money on that.
 

Papabravo

Joined Feb 24, 2006
14,409
Anything that involves multiple 24 bit A/D converters is going to be a complex project.
Q1&A1: The semiconductor business is highly competitive and constantly changing. The concept of an industry standard that everybody would use is a complete fiction. By the time you get done with the engineering, fabrication, and testing of a prototype design the industry has moved on.
Q2&A2: I used to work in high end audio, so I have some familiarity with nosebleed type prices. The money was in the packaging and the power supply. It certainly was not in the digital or analog electronics which was maybe two decades old in 2008. The units were assembled by hand and labor has been expensive for quite some time.
 

MrChips

Joined Oct 2, 2009
21,855
Q1 - Yes, every ADC is different. There is no such thing as "best" in most aspects of electronics. There is always a compromise between competing factors.

Q2 - Can an electronics engineer with a couple of years experience in the field slap together a decent audio interface? Yes.
However it is a question of how "decent".

Firstly, there is the selection of the ADC. It is not as simple as selecting the number of bits and sampling rate. There is a long list of important device parameters that is too long to list here.

Yes, most audio interfaces require an analog preamp. Again there is no such thing as the "best" preamp design.

Finally, there is another long list of important factors that have to be considered that only a knowledgeable and experienced audio engineer cares and thinks about, simple but not obvious things such as board design, packaging, connectors, power supplies, EMI, LF + RF suppression, etc.
 

Thread Starter

Dolmetscher007

Joined Mar 21, 2019
29
Q1 - Yes, every ADC is different. There is no such thing as "best" in most aspects of electronics. There is always a compromise between competing factors.
Yeah, I know there is no such thing as the "best" of almost anything. I was being a bit hyperbolic there.

Q2 - Can an electronics engineer with a couple of years experience in the field slap together a decent audio interface? Yes.
However it is a question of how "decent".

Firstly, there is the selection of the ADC. It is not as simple as selecting the number of bits and sampling rate. There is a long list of important device parameters that is too long to list here.

Yes, most audio interfaces require an analog preamp. Again there is no such thing as the "best" preamp design.
I am not an electrical engineer with years of experience, but I am a stubborned amateur that would like to try! Lol!!! Why not, right? Ya gotta start somewhere. The worst thing that can happen is I waste a few hundred bucks on evaluation boards and components only to fail and have a much deeper appreciation for these types of devices that I think I kind of take for granted.

I have no desire to get into pre-amp design. That wheel has been invented, and all the factors surrounding it are so esoteric and meta. Plus, I already own some bad ass vintage preamps from Rupert Neve. I just want to build an audio interface that can handle two incoming channels of audio, convert it to digital, and push it into my computer over the Thunderbolt protocol.

Finally, there is another long list of important factors that have to be considered that only a knowledgeable and experienced audio engineer cares and thinks about, simple but not obvious things such as board design, packaging, connectors, power supplies, EMI, LF + RF suppression, etc.
Yeah... HERE is where I think my naivety is really showing! I can read data sheets for ADC and come up with power mgmt circuits that would, in theory anyway, work to power the ADC and the surrounding devices. But I know nothing about radio frequency suppression other than a couple of Faraday Cage videos I've seen on YouTube. Same with Electromagnetic Interference. I know what it is, from building a lot of guitar pickups. I guess, I assumed that as long as the device is enclosed in a metal housing, and any internal wires are tightly wound together, EMI and RFI would not be an issue. I don't even know what "LF" is however. I'm not sure if you are talking about Low Frequency, or Line Filtering. That should tell you something right there, that I have some studying to do. But I'll get it. I'm a persistent sum'bitch! Ha ha ha!!!

I used to work in high end audio, so I have some familiarity with nosebleed type prices. The money was in the packaging and the power supply. It certainly was not in the digital or analog electronics which was maybe two decades old in 2008. The units were assembled by hand and labor has been expensive for quite some time.
Papabravo - can you tell me, do companies like Apogee and Universal Audio design and manufacture their own ADCs? I was looking at the Apogee Symphony I/O mkII 16 - channel thunderbolt audio interface. This thing appears to be the exact type of device I am talking about. It can accept 16 channels of analog inputs, has 16 digital outputs, has zero preamps, and seems to just take incoming audio signals, convert them, and push them into a computer over thunderbolt. Obviously, there is a ton more to it. I mean, it also has an LCD screen with a multi-function digital control knob, so I am sure there is an entire proprietary operating system on this bad boy. There is also a fan on the back, so I imagine there is a CPU, DSP, or microcontroller and a dozen or so other things that I am simply not experienced enough to know about. My question for you is, when you read the marketing on this thing, they talk about Apogee's X-series and Rosetta Series converters, their Big Ben master clock, and the Symphony PCI protocol. Is all this just marketing blah? Are they actually just Texas Instruments ADCs, that maybe Apogee had them customize a couple of little things, or does Apogee actually employe a team of ADC chip designers who design ADC chip silicon topology, have a wafer-fab to dope the semi-conductors, and actually manufacture totally proprietary ICs?
 

Papabravo

Joined Feb 24, 2006
14,409
Yeah, I know there is no such thing as the "best" of almost anything. I was being a bit hyperbolic there.


I am not an electrical engineer with years of experience, but I am a stubborned amateur that would like to try! Lol!!! Why not, right? Ya gotta start somewhere. The worst thing that can happen is I waste a few hundred bucks on evaluation boards and components only to fail and have a much deeper appreciation for these types of devices that I think I kind of take for granted.

I have no desire to get into pre-amp design. That wheel has been invented, and all the factors surrounding it are so esoteric and meta. Plus, I already own some bad ass vintage preamps from Rupert Neve. I just want to build an audio interface that can handle two incoming channels of audio, convert it to digital, and push it into my computer over the Thunderbolt protocol.


Yeah... HERE is where I think my naivety is really showing! I can read data sheets for ADC and come up with power mgmt circuits that would, in theory anyway, work to power the ADC and the surrounding devices. But I know nothing about radio frequency suppression other than a couple of Faraday Cage videos I've seen on YouTube. Same with Electromagnetic Interference. I know what it is, from building a lot of guitar pickups. I guess, I assumed that as long as the device is enclosed in a metal housing, and any internal wires are tightly wound together, EMI and RFI would not be an issue. I don't even know what "LF" is however. I'm not sure if you are talking about Low Frequency, or Line Filtering. That should tell you something right there, that I have some studying to do. But I'll get it. I'm a persistent sum'bitch! Ha ha ha!!!


Papabravo - can you tell me, do companies like Apogee and Universal Audio design and manufacture their own ADCs? I was looking at the Apogee Symphony I/O mkII 16 - channel thunderbolt audio interface. This thing appears to be the exact type of device I am talking about. It can accept 16 channels of analog inputs, has 16 digital outputs, has zero preamps, and seems to just take incoming audio signals, convert them, and push them into a computer over thunderbolt. Obviously, there is a ton more to it. I mean, it also has an LCD screen with a multi-function digital control knob, so I am sure there is an entire proprietary operating system on this bad boy. There is also a fan on the back, so I imagine there is a CPU, DSP, or microcontroller and a dozen or so other things that I am simply not experienced enough to know about. My question for you is, when you read the marketing on this thing, they talk about Apogee's X-series and Rosetta Series converters, their Big Ben master clock, and the Symphony PCI protocol. Is all this just marketing blah? Are they actually just Texas Instruments ADCs, that maybe Apogee had them customize a couple of little things, or does Apogee actually employe a team of ADC chip designers who design ADC chip silicon topology, have a wafer-fab to dope the semi-conductors, and actually manufacture totally proprietary ICs?
High end audio is a specialty business with high margins and low volumes. Our run rate could never justify a custom chip under ANY conceivable circumstances, I could never see the need for it. there is a huge amount of good stuff out there, you just have to find it.
 
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