# Focusrite 2i4 Sound Card Calibration



## coyotearms (Jul 3, 2008)

This is my first post, so before I get too far along, I really want to thank John Mulcahy and all the other wonderful folks that have worked so long and hard to make such an incredible program available to the community! 

I started using REW yesterday after reading a mouth full. I had to struggle a bit to do the sound card calibration, eventually succeeded, but have a question about using the timing reference channel. I did the calibration both ways, and they came out exactly the same. I don't know whether that means I should just use the .cal curve for the case of no loop-back on the "other" channel, or do all measurements with the loop-back always in place?

Also, could someone tell me how to interpret the phase curve, especially if it deviates significantly from zero as mine does at lower and higher frequencies?









Secondly, I did not find much help on this forum for sorting out my initial problems with the 2i4, so I though I would put here what I did to make things work. Most of the problem was due to the 2i4's rather rich means of getting signals in and out with all its physical knobs and switches. This is on a Dell XPS M1210 running Win7 x64.

I decided to use the ASIO drivers over Java after playing around with each. I like ASIO because it seems to be more informative on which inputs and outputs are chosen (there are inputs 1 and 2, and outputs 1 to 4, complicated by the fact that outputs 1 and 2 each have two physical jacks, one balanced and variable and one unbalanced and fixed!). But ASIO also gives the ability to use different devices for input and outputs as I might find out my NuForce 192S USB-to-S/PDIF handy for output of test signals to the AVR? Also, I observed REW through ASIO recognizes the si4's MIDI interface for possible EQ uses. All this sounds really cool!

To do the sound card calibration I put loop-back connections between input and output of channel 2 (right, signal) and channel 1 (left, for reference timing). Somewhere I thought I read that right should be the mic channel. Both connections were made with RCA male-to-RCA male cables. Only the 1/4" jacks were used, all with 1/4" mono plugs-to-RCA female adapters inserted. Even though those input and output jacks that are 1/4" work quite differently, I verified with the manual that the above arrangement is valid for all. Also note the 1/4" outputs are the only two of the total of six that are variable. Under the Soundcard Tab where the sound card calibration is carried out, the only things that can be changed under ASIO control is the sample frequency (set to 48000 Hz), Sweep Level (left at -12 dB) and check boxes for Invert and High Pass, both unchecked. 

Note a couple of glitches. As soon as ASIO was chosen for the driver a "Buffer size warning" window appeared that said "The ASIO driver is using a buffer (latency) setting of 442 samples, use a buffer of at least 512 samples for lower risk of glitches." Humm, didn't know where to adjust that, so I proceeded having faith that 442 is not too far off 512 and the 2i4 is supposedly a high quality well proven device in many applications! ANYONE KNOW THE BEST WAY TO DEAL WITH THAT WARNING? Also, early into messing around I would see the sample frequency choice gray out, and attempts to change it by double clicking on the "ASIO Control panel to reveal the "Foucusrite USB 2.0 ASIO Driver" window failed. I rebooted the computer with the Focusrite the only device plugged into any of the four built-in USB Ports, and after that no more surprises. 

Once the calibrate procedure got to the point where the 1kHz signal is generated, REW's Out-meter read -12 dB. To get the In-meter to equal that the front panel settings that accomplished the task: DIRECT MONITOR knob fully clockwise to its playback position, the STEREO/MONO switch set to STEREO, the large MONITOR knob set to the 12 o'clock position, both input LINE/INST switches set to INST (higher gain), both PAD buttons un-depressed (not lit, less attenuation) and each GAIN knob turned clockwise to the point that REW's In-meter and In Ref-meter also read-12 dB. DONE! With those settings the calibration curves (attached) were generated. Hope that helps anyone having trouble with the 2i4.


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## JohnM (Apr 11, 2006)

Looks good. Loopback is ignored for soundcdard cal measurements. The phase response variation is entirely normal and a consequence of the frequency response variation.


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## jtalden (Mar 12, 2009)

coyotearms said:


> ...I have a question about using the timing reference channel. I did the calibration both ways, and they came out exactly the same. I don't know whether that means I should just use the .cal curve for the case of no loop-back on the "other" channel, or do all measurements with the loop-back always in place?


The soundcard calibration process calibrates only using the measurement channel. So it requires the loopback cable. Any selected "timing reference" channel will be ignored for soundcard calibration purposes. A loopback cable on that channel will have no effect on the calibration. [REW will still apply that same calibration curve to another channel as well. So if you later change your selection to another measurement channel, the calibration file selected will be used there as well.] The timing reference channel it does not need to be individually calibrated as no measurements are taken there. It is only used for consistent timing reference from one measurement to another. Timing reference is only used for certain purposes, e.g., identifying time delays needed between a TW-MF driver or a main speaker to SW. 



> ...Also, could someone tell me how to interpret the phase curve, especially if it deviates significantly from zero as mine does at lower and higher frequencies?


Your SPL and Phase chart for your soundcard are very typical. After calibration REW will now apply the correction to any future measurements taken. So if you want to see the final result of the calibration (always a good idea), you can just take a another measurement with the loopback cable attached to the measurement channel. The SPL and Phase will then look much improved. [remember to adjust the chart scaling to the same range for the comparison.]



> ...As soon as ASIO was chosen for the driver a "Buffer size warning" window appeared that said "The ASIO driver is using a buffer (latency) setting of 442 samples, use a buffer of at least 512 samples for lower risk of glitches." Humm, didn't know where to adjust that, so I proceeded having faith that 442 is not too far off 512 and the 2i4 is supposedly a high quality well proven device in many applications! ANYONE KNOW THE BEST WAY TO DEAL WITH THAT WARNING?


The ASIO4ALL setup box has the ability to set buffer size. Just click the "ASIO Control Panel" button in REW preferences. 

Is see JohnM commented already, but just in case this helps...


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## coyotearms (Jul 3, 2008)

Thanks guys! That helps understanding the use of the separate channel with loopback for measurements but not for calibration, and I did get the same result without it and with box under the Analysis Tab checked to use it.

THE PHASE THING:
I am still a little fuzzy about the phase graph showing so much phase at low frequencies. Since phase is delay, I expected it would be higher at shorter wavelength. It does start deviating some at high frequency, yes, but more so at low. But I should not be concerned since the RESULT of applying the corrections shown below when I did the check from the Measurement Tab as you suggested looks really, really good:









THE ASIO THING:
I am still unclear about the buffer size warning. When I installed the driver package for the Focusrite 2i4 it installed its own ASIO driver. When I click on the REW ASIO Control Panel, a window opens whose title is "Focusrite USB 2.0 ASIO driver." There are two labeled sections in that window. One is labeled "Global Settings," which shows a "Bufffer Length" slider that goes up to 10 ms, AND by default is AT 10 ms. I am sure that time corresponds to some buffer size, but apparently less that 512 for me to get the warning I indicated. The other section is labeled "ASIO," has a box to change Sample Rate and indicates (but not changeable) "Input Latency 0.0" and "Output Latency 0.0." In addition it has an "about" button that indicates ASIO Driver Version 2.5.1 (Debug) and WDM Driver Version 0.0.0.0 (Debug). I do not know what WDM or (Debug) mean, and do not know if I should completely uninstall that driver package and install ASIO4ALL instead---or whether ASIO4ALL was installed as part of the REW installation. Mind you, I have been happily using the 2i4 for digitizing vinyl with the same driver package, and it has been working just fine. ANY SUGGESTIONS? Should I just bail out of using ASIO and use the Java drivers? This might be a question only John can answer. I am really glad both of you responded to my previous post!


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## EarlK (Jan 1, 2010)

*ASIO4ALL *  must be downloaded & then installed separately .

There's no need to uninstall your current 2i4 driver just to use ASIO4ALL . 

One just selects ASIO4ALL as the preferred ASIO driver from within REW's preferences window ( after one chooses ASIO instead of JAVA ) .

Here's what the ASIO4ALL control panel looks like ( setup to give REW what it wants when I use my Scarlett 2i2 ) .










:sn:


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## jtalden (Mar 12, 2009)

coyotearms,
A 10 ms latency at a 44100 sample rate corresponds to a 441 sample buffer size [44100 samples/s * 0.010 s = 441 samples (buffer size)]. So you could just increase the latency setting in the Focusrite panel.

ASIO4ALL is a good option also - use whichever you like. 

I do not understand your question regarding phase, but... 

The focusrite audio interface, as well as all other audio interfaces and soundcards, has a reduced SPL and increasing phase at low freqs. This is due to the design of the circuitry. This design is necessary to block any DC from being passed to the output. The REW soundcard calibration compensates for this. It just subtracts the error out of the measurement so that the charts shows the actual SPL and phase of the speaker (or your wire in this case).

Your last chart shows that the SPL and Phase (dark red and light red) of the loopback measurement is now flat from 2 Hz to 20 kHz. The calibration is perfect.

The dotted line is just a vistual indication of the original soundcard SPL response that is now being compensated for. You can just clear that selection box at the bottom of the chart now that all is working well. It is no longer of any interest.


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## coyotearms (Jul 3, 2008)

Thank you both for clearing up some issues about soundcard calibration and ASIO. The ASIO problem I was having was that the driver from Focusrite and accessed by REW did not allow me to change buffer length---the only knob available for varying buffer size was by varying time up to 10ms, which was not good enough. So I bit the bullet and installed the latest version of ASIO4ALL (v2.11 Beta2). But a number of strange system level things started happening. I remembered reading a ways back that ASIO4ALL is suppose to co-exit with other ASIO drivers, so that did not seem to be the problem. Then I dropped down a notch and installed Beta1 that one of you apparently is happy with, and it worked. Far more complicated with all the bells and whistles it has, but it tolerates me. It does, however, take a little coaxing for it to see all the WDM devices.

At this point I have done enough measurements of my system with the Focusrite and RS SLM to get a feel for how to approach tweaking it while I waited for the MiniDSP UMIK-1 mic to come. I am now getting familiar with it and my existing NuForce 192S USB Audio S/DPIF output device and see what folks mean about the RS being o.k. for lower frequencies, but maybe not more than that. If I am doing things correctly, I am shocked at the variation in the spectrum at higher frequencies that are going to be challenging to sort out. I kind of expected that given that the AV system is located in a space far more complicated that a simple rectangular room! What an amazing tool REW is for digging into what is going on! Thanks again for your help.


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