Topic: AMB Labs Gamma2 DAC Measurements (y2) (Read 3634 times)

OJneg · « **Reply #10 on:** May 02, 2014, 01:14:14 AM »

It's interesting to look at these measurements next to AMB's. Keep in mind his signal path is much different. Coax input and with ASRC chip are at work in his measurements. And he's also using 24/96 on the input, rather than 16/44.1 (which USB is restricted to)

Looks like both the noise floor and crosstalk are a good 10dB higher than what his tests indicate. I thought that might be a USB thing, but it looks like it's the noise floor of your ADC creepin' in. (If your loopback measurements in the other thread are accurate) Actually, the gamma2 even surpassed the measured performance of AMB's M-Audio Firewire audio interface in most areas so it shouldn't come as a terrible surprise. So in actuality, I'd expect most of those results (specifically noise, crosstalk, and THD) to be even lower than your test showed. Hard to be sure unless some very precision gear is used to test.

Except for the roll-off on the very top, I'd say the gamma2 surpasses your interface as well. Note the wee bit of roll-off on the low end must be from your device's coupling cap (although the gamma2 is cap coupled as well).

Jitter is an interesting thing. AMB specifies .5ps (1ps max) of jitter, but that's only with the ASRC chip being used. Somehow (maybe someone else could chime in), use of that ASRC chip greatly reduces measured jitter. Not sure with how to interpret those results though; Is there a way to get some sort of direct read-out with JTest?

Also worth noting the nature of the gamma2's distortion character. Higher order components are absent, and the level of each component is decreasing with order (which is often something to look for when designing audio gear). Look at the SB1240's or M-Audio's distortion character in comparison and you'll see higher-order components sprinkled throughout.

With regard to the digital filters, I think it's important how both A and B are better at rejecting ultrasonic stuff. I'd wager that this (combined with the distortion character) is part of the reason that the gamma2 has such a smooth character to it. Very digititus free compared to other cheap DACs IMO.

The last thing I would mention is that the early roll-off in the treble isn't as bad as it looks. While Mode C does give more "air" in a loose sense, it doesn't make the DAC any more resolving or detailed really. Just a bit more presence when it comes to cymbals and stuff. OTOH, both A and B's presentation of the rest of the spectrum was superior IMO, making it a small price to pay for playback and listening.

firev1 · « **Reply #11 on:** May 02, 2014, 03:45:24 AM »

I would hold my breath till a 24 bit test could be done as only then can THD test reveal distortion below the 16 bit noise floor, the THD for the price is still friggin good though. Stereo Crosstalk is indeed a limitation of the 1240, max out at 96db.

As for jitter to my knowledge, there is no way to get a direct read out, the only way is to guesstimate and sum the products manually. I would say though that jitter here looks like adaptive isochronous usb, not as good as the usb implementation on the ODAC and async implementations. There is also a bunch of low frequency jitter causing a spread in the base of the fundamental signal. I wonder if these characteristics might improve with 24 bit data(I have not done 16 bit Jtest ever). I think the low frequency jitter is inherent of the Gamma 2 though usb or not, take a look at the 1khz graphs on AMB's site, some spreading in the base of the signal which is not as tight as the ODAC or SB1240.

For measuring the local clock, I reckon they are quoting spec sheet or have a high resolution jitter analyser(less likely).

OJneg · « **Reply #12 on:** May 02, 2014, 04:07:31 AM »

Adaptive isochronous is correct. Possible benefits to be had in terms of jitter with coax source, or better USB input.

24 bit tests aren't going to happen. As I said, the USB input is limited to 16/44.

Hands · « **Reply #13 on:** May 02, 2014, 07:00:29 AM »

Quote from: mechgamer123 on May 01, 2014, 11:15:49 PM

Could you explain what the different filters are, and why filter C has much better extension than the other two?

Different digital filters for the oversampling process that takes place in the DAC. My understanding is not good enough to explain well, but the type of oversampling/filtering used affects the frequency response and other characteristics (i.e. the frequency domain). On the other hand, certain filters introduce pre and/or post-ringing into the equation, thus affecting the time domain. I've commonly been told that either A) this ringing isn't audible and/or B) pre-ringing is usually shown on impulses that aren't natural to music, but I think there is a clear, but subtle, audible difference between different digital filter methods.

I have found that I don't particularly care for linear-phase filters, or those with pre and post-ringing. Likewise, I find it hard to differentiate linear-phase with a strong minimum-phase filter, that being one with a lot of post-ringing. I really like the minimum-phase filter implemented in this scenario. Very short post-ringing. That said, I don't think the DAC sounds bad at all with filter C (strongest linear-phase filter to pick from), but I just prefer B. A is pretty close to B as well. However, some people have the opposite preference as me, and that's fine. You can read more about my subjective thoughts on the filters in my DAC impressions thread.

Quote from: OJneg on May 02, 2014, 01:14:14 AM

What OJ said, because my formatting gets messed up every time I post something...took out all his new lines.

Yup, that's exactly right. We're touching on the limits of what my ADC can do and what you can get from 16-bit audio (my ADC is kept at 24/96 for most of these tests). I can't remember if I updated my loopback measurements of the SB1240, but DACs like this and the X-Sabre tend to max it out. If my ADC gets maxed out, the DAC probably performs well enough for me to not care objectively and, thus, really only focus on subjective traits. The bass roll-off is from my ADC, as mentioned in my first posts. But, overall, the Gamma2 performs very well, especially with distortion.

The treble roll-off really isn't that bad. Filter C brings a bit more detail and air, but, personally, I think it gives a poorer timbre and less body to the sound (personal preference). I really, really like how this DAC sounds with filter B, despite its limitations to USB and 16/44.1. It is a touch dark, but very smooth, on A and B. It is a damn good listen, and I am sad to see it go.

mechgamer123 · « **Reply #14 on:** June 07, 2014, 09:07:44 AM »

@hans, I couldn't find your impressions post in the DAC impressions thread, mind linking me?

I'd just like to post my impressions here (unless I should just post them in the DAC impressions thread instead?). Huge thanks to OJ for letting me listen to this little beast!

Quoted from PM to Oj: "I'm sold on this DAC. I think I'll definitely build one once I get the spare cash over the summer. Like you said, it's a very smooth sounding DAC. I didn't really bother listening for detail levels (since I don't feel confident enough in my ability to discern actual differences and BS I'm just making up in my head) but the instrument separation sounded just a touch worse than the CS4398 I was comparing it to. However, with my STAX Lambda SR-202 and SRM-212 amp, which sound a little bit harsh being run out of the CS4398, and frankly a lot of other DACs I've heard, the smooth sound signature really tames the harshness down to where I can't really even detect it, but it doesn't sound so shitty and rolled off as other "warm" sounding DACs I've tried that just sound dull and boring. "

Hands · « **Reply #15 on:** June 07, 2014, 11:01:24 AM »

No problem! Here's where I started my Gamma2 impressions: http://www.changstar.com/index.php/topic,1535.msg40729.html#msg40729

OJneg · « **Reply #16 on:** August 14, 2014, 01:29:53 AM »

Here's my own run through of the gamma2's measured performance. This is the same unit that hans measured but there's a different signal path here. See attached file. Unzip the .zip file first and make sure the .htm file and the unzipped image folder are in the same directory.

* FR: Slow roll-off filters (A & B) exhibit early roll-off

* Noise and DR: The readouts are limited by 16bit word length. But as can be seen on the noise level plot, this is a very quiet DAC. Keep in mind that while is very much a non-ideal testing scenario the gamma2 performs well; the USB input is driven from the rear of a messy desktop with plenty of other devices on the bus and the line-in is being run across a few mains lines and near an EI transformer. Possible benefits to be gained with independent LPS yet.

* THD and IMD: Comparing these plots vs. Ti's or Hans' is revealing. I'd speculate that the gamma2's analog output performance usurps that of most line-in stages. Other test systems just aren't revealing it. Very impressive.

I suspect any weaknesses of the gamma2 would lie on the digital side, specifically the gamma1 USB input. Hans' jitter measurements hinted at this. Might be interesting to compare the performance after I install the ASRC.

Hands · « **Reply #17 on:** August 14, 2014, 12:53:10 PM »

Such an awesome, little DAC. One of my favorites out of the DACs I tried in that time period. I thought it sounded great without the ASRC, but, given my tastes, I probably would prefer the sound without it myself.

Author Topic: AMB Labs Gamma2 DAC Measurements (y2) (Read 3634 times)

OJneg

Re: AMB Labs Gamma2 DAC Measurements (y2)

firev1

Re: AMB Labs Gamma2 DAC Measurements (y2)

OJneg

Re: AMB Labs Gamma2 DAC Measurements (y2)

Hands

Re: AMB Labs Gamma2 DAC Measurements (y2)

mechgamer123

Re: AMB Labs Gamma2 DAC Measurements (y2)

Hands

Re: AMB Labs Gamma2 DAC Measurements (y2)

OJneg

Re: AMB Labs Gamma2 DAC Measurements (y2)

Hands

Re: AMB Labs Gamma2 DAC Measurements (y2)

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Author Topic: AMB Labs Gamma2 DAC Measurements (y2) (Read 3634 times)