• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Advice on USB ADC and Analysis Software please

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
#1
I'm looking at doing some playing around to measure frequency response of some equipment. In particular analogue vs digital EQ, and the effect of changing valves (sorry, tubes) in a headphone amp. Can anyone recommend a good USB ADC for measuring the RCA line out (doesn't have to be super accurate, just repeatable, budget say $100-$200) and capture/analysis software? REW sounds like it may be pretty handy. The configuration I'm envisaging is laptop - DAC - device under test - ADC - laptop. May need to have the ADC in parallel with headphones (not sure if the headphone impedance will change the overall frequency response or not, this will be one of the tests).
 
OP
R

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
Thread Starter #2
Decided on an ADC - a Focusrite Scarlett Solo. Has pretty good specs, plus a high and low level input so I can use it with a microphone on the next project of room equalization as well. Also has adjustable gain and a headphone monitor output which could be useful.
Line Input: Frequency Response 20Hz - 20kHz ± 0.1dB, Dynamic Range110.5dB (A-weighted), THD+N<0.002%, Maximum Input Level 22dBu (at minimum gain), Gain Range56dB, Impedance60kΩ
 

Blumlein 88

Major Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
11,434
Likes
16,709
#3
Did not notice your first post. The Solo should do what you want.

I do think you'll want the headphones in parallel for your purposes.

REW should do what you want it to do. It will capture frequency response differences, along with distortion in a simple sweep. It also offers most of your other common types of measurement which can be done one at a time. Plus uncommon things like measuring a tone and showing not just the distortion levels of the harmonics, but their phase too.

You might also at some point find Pkane's free software Deltawave useful. It lets you take two files captured and compare the differences between them using music for the signal. It does many things so a little time just messing around with it is helpful. I'd give the same advice with REW if you aren't familiar with it yet.

Here is where to get Deltawave:
https://deltaw.org/

Here is a thread from when Paul first started offering the software.
https://www.audiosciencereview.com/...test-deltawave-null-comparison-software.6633/
 
OP
R

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
Thread Starter #4
Did not notice your first post. The Solo should do what you want.

I do think you'll want the headphones in parallel for your purposes.

REW should do what you want it to do. It will capture frequency response differences, along with distortion in a simple sweep. It also offers most of your other common types of measurement which can be done one at a time. Plus uncommon things like measuring a tone and showing not just the distortion levels of the harmonics, but their phase too.

You might also at some point find Pkane's free software Deltawave useful. It lets you take two files captured and compare the differences between them using music for the signal. It does many things so a little time just messing around with it is helpful. I'd give the same advice with REW if you aren't familiar with it yet.

Here is where to get Deltawave:
https://deltaw.org/

Here is a thread from when Paul first started offering the software.
https://www.audiosciencereview.com/...test-deltawave-null-comparison-software.6633/
Thanks - I've starting looking at Audacity which looks like it will be good for single tones and white noise. Hadn't really thought about distortion measurement, but since the Solo has reasonable specs I'll start exploring distortion with REW as well. Final stage will be some real music so Deltawave will get a run as well.
 

Blumlein 88

Major Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
11,434
Likes
16,709
#5
Thanks - I've starting looking at Audacity which looks like it will be good for single tones and white noise. Hadn't really thought about distortion measurement, but since the Solo has reasonable specs I'll start exploring distortion with REW as well. Final stage will be some real music so Deltawave will get a run as well.
Oh yeah, Audacity is very handy. It also has some gotchas. REW will do noise of several varieties and it lets you choose tones. It does more than a sweep. I also think the quality of results with REW is going to be a step above. Even though I'm an Audacity cowboy myself.
 

RayDunzl

Major Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
11,073
Likes
10,950
Location
Riverview FL
#6
REW for analysis,

Audacity mainly for recording here.
 
OP
R

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
Thread Starter #7
Oh yeah, Audacity is very handy. It also has some gotchas. REW will do noise of several varieties and it lets you choose tones. It does more than a sweep. I also think the quality of results with REW is going to be a step above. Even though I'm an Audacity cowboy myself.
REW it is then - thanks
 
OP
R

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
Thread Starter #9
Started playing with REW - attempting to test the frequency response of a piece of wire ie output of PC (internal Realtek DAC) connected straight to input of Focusrite Scarlett Solo
realtek to focusrite baseline rew.jpg
Magnitude response is way better than I thought it would be, accurate enough to start comparing frequency response of my headphone amp. Phase response is a bit weird, so I tried a different configuration - cheapo USB dongle DAC connected straight to input of Focusrite Scarlett Solo
dongle to focusrite baseline rew.jpg
Magnitude looks a bid dodgy now, and phase is even worse but still follows the same trend as before so there may be a limitation with the Focusrite ADC for phase accuracy over a few kHz.
 

AnalogSteph

Major Contributor
Joined
Nov 6, 2018
Messages
1,318
Likes
1,167
Location
.de
#10
I think the glitches may be related to either literal buffering issues or sample rate betwen playback and recording device being slightly out of sync (I would assume the Scarlett has a clock reference of its own, as may the dongle, and the Realtek is likely to be sync'd up to some internal clock, all with more or less PLL action to get the desired sample rates). I have no idea how REW reacts to such; some tests in RMAA don't like it for sure. When using REW you should probably switch to ASIO I/O and use ASIO4All for the other devices as well, otherwise you'll have to keep track of sample rates in multiple places.

The "waves" in the phase response are likely to reflect the passband ripple of IIR filtering - perhaps the ADC's, given that the Solo uses a CS4272 and Cirrus Logic are well-known for using partial IIR filtering in their converters. You can't see the passband ripple in the magnitude among all the noise and glitches (some tweaking of REW settings may be required to get accuracy up first), it would be <0.1 dB peak.

If you want to get a good baseline, you better start off with plain loopback testing.
 
OP
R

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
Thread Starter #11
I think the glitches may be related to either literal buffering issues or sample rate betwen playback and recording device being slightly out of sync (I would assume the Scarlett has a clock reference of its own, as may the dongle, and the Realtek is likely to be sync'd up to some internal clock, all with more or less PLL action to get the desired sample rates). I have no idea how REW reacts to such; some tests in RMAA don't like it for sure. When using REW you should probably switch to ASIO I/O and use ASIO4All for the other devices as well, otherwise you'll have to keep track of sample rates in multiple places.

The "waves" in the phase response are likely to reflect the passband ripple of IIR filtering - perhaps the ADC's, given that the Solo uses a CS4272 and Cirrus Logic are well-known for using partial IIR filtering in their converters. You can't see the passband ripple in the magnitude among all the noise and glitches (some tweaking of REW settings may be required to get accuracy up first), it would be <0.1 dB peak.

If you want to get a good baseline, you better start off with plain loopback testing.
Thanks - will do some more experimenting
 
OP
R

rkbates

Member
Forum Donor
Joined
Jul 24, 2020
Messages
79
Likes
79
Location
Down Under
Thread Starter #12
Glitches all gone - now using the Focusrite Solo for both generating the analogue signal and recording it's own signal via hardwire loopback, hence same timing source for both. Changed to ASIO drivers in any case so now good to start measuring some actual equipment.
focusrite loopback.jpg
 
Top Bottom