Researching state of the art audio ADC performance

[Wes]

Which is why there isn't a big push to plumb the physical limits of ADCs.
Don't know I've ever seen any specs, but along with the Prism Dream, many consider the Pacific Microsonics to be the best of the best ever. I do seem to recall a loopback with a PM model 1 ADC and DAC hit something like -120 db nulls with music. I don't recall anything else getting close to that that I've ever heard about or read about.

I keep hearing this, but what was so great about the Pacific Microsonics other than low noise ?

 

[Blumlein 88]

I keep hearing this, but what was so great about the Pacific Microsonics other than low noise ?

I seem to recall it was low noise and distortion, perfectly flat FR or nearly so, and unusually good phase response to rather near the limits of the sample rate. Other than that you'll have to ask those who continue to use them in studios.

 

[Blumlein 88]

Here is a good simple presentation on some common mic preamp topologies. Which I suppose is a bit off topic for ADCs.

http://www.thatcorp.com/datashts/AES129_Designing_Mic_Preamps.pdf

The pink and green curves are close to what I've seen testing a few mic preamps.

This couple pages is also worth reading on mic pres.
https://sound-au.com/project66.htm

 

[AnalogSteph]

I seem to recall it was low noise and distortion, perfectly flat FR or nearly so, and unusually good phase response to rather near the limits of the sample rate. Other than that you'll have to ask those who continue to use them in studios.

These cost $16k, and they were sold at cost. Some serious engineering inside I'm sure. Converter hybrids, high supply voltages, DSP (for HDCD encoding and decoding if nothing else), the whole nine yards. The front panel design hasn't aged half-badly either, IMHO.

Specifications for the later Model Two (which went up to 192k, the Model One was 44.1/88.2 only) are rather terse, but the HDCD Signal Processing section provides a glimpse of the complexity inside:

Eight Motorola 56009 DSPs and one Pacific Microsonics PMD-100 HDCD decoder ASIC control A/D conversion, sampling rate conversion, word length conversion, digital gain adjustment, HDCD encoding and decoding and D/A conversion.

Eight 56k DSPs. I don't think I've ever sighted more than two DSP chips in any consumer-grade equipment.

Also, the thing seems to be built like an absolute tank:

Weight
Processor Unit: 35 lbs. (16 kg.)
Power Supply: 20 lbs. (9 kg.)
Custom ATA Case: 41 lbs. (19 kg.)

Now, as much fun as it is to marvel at the SOTA of days past, I sure am glad that merely good converters have gotten way more affordable and power-efficient over the years. These days you can get a 120 dB(A) hi-res DAC / headphone driver the size of a pen and operating on USB bus power (if consumer-level with 1 Vrms out max) for $99. (IL-DSP, based on this guy.) That's pretty close to "the computer is the bump in the power cord" terrain and rather amazing in its own right.

 

[Blumlein 88]

This is off topic for the thread, but in topic with recent discussion.
Measured the EIN of the Antelope Zen Tour microphone preamps I have. I think the chart is self explanatory. This is using 100 ohms of resistance as a source. The noise over 20 khz for that should be around -132.7 dbu (-138 dbu A-wtd). You can see mostly this pre has EIN of -130 dbu between 30 and 65 db of gain. There is something weird at the 5 db gain setting, but it does this with a short or with higher resistance.

Max input on the microphone pre is 8.2 dbu or right near 2 volts. These are not A-wtd values. Doing so would make them around 3 db better.

 

[GTAXL]

I seem to recall it was low noise and distortion, perfectly flat FR or nearly so, and unusually good phase response to rather near the limits of the sample rate. Other than that you'll have to ask those who continue to use them in studios.

Can you provide a link or screenshot of these measurements? I'd love to see the Pacific Microsonics measured.

 

[Blumlein 88]

Can you provide a link or screenshot of these measurements? I'd love to see the Pacific Microsonics measured.

I'll see if I can find them, but don't hold your breath. Those are rare pieces only something like 100 of them made and working examples fetch well above $10k as most are used in studios.

 

[GTAXL]

I'll see if I can find them, but don't hold your breath. Those are rare pieces only something like 100 of them made and working examples fetch well above $10k as most are used in studios.

Hold my breath on the measurements or getting a unit? I have a few friends that have a Pacific Microsonics Model 2.

 

[Blumlein 88]

Hold my breath on the measurements or getting a unit? I have a few friends that have a Pacific Microsonics Model 2.

I don't remember where the measurements were. I think they were part of some threads at Gearslutz. I'll see if I can find them. If you know someone with them, then you are lucky. Do they have any good gear to measure them? Or if they have adc and dac they could do loopbacks with them.

 

[rdenney]

Back on topic, and for posterity on this mildly stale thread.

The Benchmark ADC1 is still pretty close to SOTA for anything mortals can afford. S/N is 121 dB, THD+N is -104 dB at -3 dBFS input.

It has two gain stages. The first has three settings: unity, +10, and +20. The second is variable, using either an external pot or an internal pot reachable by screwdriver, selectable by switch, both with a range of 0 to +24 dB. The 44 dB total gain isn’t enough for condenser mics in my experience, and it doesn’t have phantom power, so that isn’t the target use case. Balanced XLR inputs. Outputs include optical, two coax, XLR, and USB, all fed simultaneously. Both 16 and 24-bit dithered outputs simultaneously. Alternate clock inputs, but uses USB to align to computer clock. Software-controlled bit depth and sample rate on USB, but that doesn’t affect other digital outputs, which can go up to 24/192. This may not be as high as some go, but it’s far higher than is actually useful in audio applications.

To me, the flexibility of gain control is as important as measured specs. I like stuff with knobs. This is a stereo ADC that would serve just fine in a mastering situation. I use it for digitizing all my analog sources.

Rick “pretty good considering its age” Denney

 

[AnalogSteph]

There is little doubt in my mind that for its intended purpose - audio recording - a good studio-level AK5394A-based ADC like the ADC1 is extremely hard to improve upon. SOTA for converter chips has moved on by 7 dB tops (it was at a very high level even 20 years ago), the aforementioned level adjustments permit covering ~140 dB worth of total (non-instantaneous) dynamic range or more, and you have to get >120 dB of instantaneous dynamic range through your system somehow in the first place.

I can nonetheless think of some scenarios that even a unit like this would struggle to handle, but they would be pretty extreme, like recording with some Rode NT1s or Sennheiser MK4s or similar inside an anechoic chamber using an Earthworks ZDT series preamp. A measurement application probably is a more realistic challenge: You would already need some tricks to verify the performance of current SOTA DACs with their dynamic range around 130 dB and distortion products that can be as low as 130 dB down (THD+N -125 dB or so).