I need a USB audio interface with good objective measured specs and at least 96 Ksamples/sec capability, for measuring speakers and other audio equipment. I'd like one which allows me to set mic gain precisely, so I need something which has a digital display of the mic gain. Which USB audio interface should I get?
A bit of background. I've been designing speakers off and on for almost twenty years, and I've used Speaker Workshop, then ARTA, for SPL measurements. I used to use SW with an impedance jig for impedance measurements, now I use DATS. I used to use SW for crossover modelling, I now use VituixCAD. You get the general idea -- I'm not a complete newbie.
I use a Focusrite Scarlett 2i2 and a Behringer ECM mic calibrated from Cross Spectrum Labs, for my SPL measurements, and it is great, but for one missing feature -- I'd like to set mic gain very accurately and repeatedly between sessions. In other words, if I turn the mic input gain control knob today and set the gain to a specific setting, I should be able to come back tomorrow and set the knob to exactly the same gain. I need accuracy to a fraction of a dB.
The reason for this is I sometimes work on a whole set of similar speakers, or I want to do a lot of measurements, and I can't finish all the measurements in one morning. Therefore, in such cases, I can't measure multiple drivers with the exact same gain settings. If my audio interface had a digital display to let me set the gain exactly to a fraction of a dB, I would be able to make reproducible speaker SPL measurements across multiple sessions.
Any suggestions?
A bit of background. I've been designing speakers off and on for almost twenty years, and I've used Speaker Workshop, then ARTA, for SPL measurements. I used to use SW with an impedance jig for impedance measurements, now I use DATS. I used to use SW for crossover modelling, I now use VituixCAD. You get the general idea -- I'm not a complete newbie.
I use a Focusrite Scarlett 2i2 and a Behringer ECM mic calibrated from Cross Spectrum Labs, for my SPL measurements, and it is great, but for one missing feature -- I'd like to set mic gain very accurately and repeatedly between sessions. In other words, if I turn the mic input gain control knob today and set the gain to a specific setting, I should be able to come back tomorrow and set the knob to exactly the same gain. I need accuracy to a fraction of a dB.
The reason for this is I sometimes work on a whole set of similar speakers, or I want to do a lot of measurements, and I can't finish all the measurements in one morning. Therefore, in such cases, I can't measure multiple drivers with the exact same gain settings. If my audio interface had a digital display to let me set the gain exactly to a fraction of a dB, I would be able to make reproducible speaker SPL measurements across multiple sessions.
Any suggestions?
The Focusrite products are incredible bang for the buck. Can't you just leave the gain knob alone between measurements? Alternatively, maybe a mic preamp with fixed gain is the trick. Just feed the output of that to the Focusrite line input.
Tom
Tom
@tomchr I agree, the Focusrite products are great. My problem with long measurement sessions is that I don't have a workshop -- I usually have to work for half a day, pack up and clean up, then work again the next day, etc. It's really a pain if I have to ensure that I physically never touch the two mic gain knobs in the interim.
I'm embarking on some trial projects where I'll be fitting a whole range of mids and midbass drivers on trial enclosures and taking measurements, so that I can keep those measurements as a kind of reference for future projects. If this trial has to be useful, then the relative SPL of all the drivers need to be accurate, so that, on a future date, I can simply pick up midbass A and tweeter B and make a speaker out of them without needing to re-measure them.
Now this trial measurement festival will go on for days. I have a dozen drivers to work through. So, you see what I'm faced with? Specially without a dedicated workshop space?
@silverprout thanks. I was looking at the MOTU products too. From the website, I could see that the master gain control setting is displayed in the display panel, but do the individual mic gains also get measured and displayed?
Edit: The link you posted took me to a product page which has a YouTube video review. The reviewer twiddled the mic gain knobs while the unit was on, and the display did not seem to show any digital readout of gain, only the VU signal levels. So I don't think this unit will do the trick for me.
I'm embarking on some trial projects where I'll be fitting a whole range of mids and midbass drivers on trial enclosures and taking measurements, so that I can keep those measurements as a kind of reference for future projects. If this trial has to be useful, then the relative SPL of all the drivers need to be accurate, so that, on a future date, I can simply pick up midbass A and tweeter B and make a speaker out of them without needing to re-measure them.
Now this trial measurement festival will go on for days. I have a dozen drivers to work through. So, you see what I'm faced with? Specially without a dedicated workshop space?
@silverprout thanks. I was looking at the MOTU products too. From the website, I could see that the master gain control setting is displayed in the display panel, but do the individual mic gains also get measured and displayed?
Edit: The link you posted took me to a product page which has a YouTube video review. The reviewer twiddled the mic gain knobs while the unit was on, and the display did not seem to show any digital readout of gain, only the VU signal levels. So I don't think this unit will do the trick for me.
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https://www.swamp.net.au/icon-aio6-usb-audio-midi-device-and-control-surface
I don't know if this will do it, but this thing ticks some serious boxes for the money. Amazing amount of comprehensive functions and abilities as well as where it can be used. If that can do what you need than it makes it for the perfect one interface solution for a small home studio, workshop environment. I have a Yamaha MG12XU that is not cutting it with IO channels over USB and digital display of info on onscreen applications. If this thing can do the speaker measurement requirements too then would be unreal
I don't know if this will do it, but this thing ticks some serious boxes for the money. Amazing amount of comprehensive functions and abilities as well as where it can be used. If that can do what you need than it makes it for the perfect one interface solution for a small home studio, workshop environment. I have a Yamaha MG12XU that is not cutting it with IO channels over USB and digital display of info on onscreen applications. If this thing can do the speaker measurement requirements too then would be unreal
How about getting a electronic calibrator? You stick your mic into the calibrator, turn it on and it makes a signal at a known level, each time you use it. Then you can fix whatever gain adjustment may have slipped from measurement session to session. That's how the pro's do it - verify the whole signal chain to a known SPL, before making a measurement.
https://www.ebay.com/itm/275232081616 About $20 shipped - the guy says he's got more than 10 of them. Hint; while they may not be calibrated to a valid NIST traceable SPL level anymore, they will very likely come on at the same SPL level, each time you use it.
I just bought one and didnt even know I needed it until I tried to solve your problem. I'm tired of making relative SPL measurements, having never had a mic calibrator. Back when, we used B&K pistonphones; apparently a mechanical SPL generator never changes...
https://www.ebay.com/itm/275232081616 About $20 shipped - the guy says he's got more than 10 of them. Hint; while they may not be calibrated to a valid NIST traceable SPL level anymore, they will very likely come on at the same SPL level, each time you use it.
I just bought one and didnt even know I needed it until I tried to solve your problem. I'm tired of making relative SPL measurements, having never had a mic calibrator. Back when, we used B&K pistonphones; apparently a mechanical SPL generator never changes...
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@Randy Bassinga Thanks. I looked at the specs, and I don't think it'll do a digital readout of the mic gain setting, I could be wrong.
@jjasniew this is very interesting, and it's inexpensive, and it does not need me to throw away my Scarlett 2i2. I am so glad you pointed me to this. Let me see what else is on offer. And you're right, I don't need it to be accurate in absolute terms, I just need it to be repeatable to a fraction of a dB.
@jjasniew this is very interesting, and it's inexpensive, and it does not need me to throw away my Scarlett 2i2. I am so glad you pointed me to this. Let me see what else is on offer. And you're right, I don't need it to be accurate in absolute terms, I just need it to be repeatable to a fraction of a dB.
A bit of Internet searching seems to indicate that this item you have pointed to is from a reputed company. They sell an SPL meter (called a dosimeter, it seems) and a calibrator as one set. https://www.ebay.com/itm/333325837715 I don't need the SPL meter, so I'll go for the calibrator. Thanks a lot, I'm about to place an order. There are others too, twice or thrice as expensive: https://www.ebay.com/itm/266048773585 and https://www.ebay.com/itm/143961529857
You guys would know more as I am only getting into this. I am hoping that since the gain might be rotary encoder based, it might be able to display what it is doing over MIDI somehow or am I on the wrong track?
I wouldn't know what information is sent over MIDI, because I won't hook up the audio interface to my laptop through any MIDI interface. I just need to hook up an analog mic to the mic input of the audio interface, and its gain is controlled from the knob near the mic socket. This knob is almost always just a pot, not a rotary encoder.
I understand what you are doing. I have been trying to get together a similar test setup on the work bench too. This is in the same room as the home studio desk. I am setting for deep DAW and computer based audio tools with multiple control surfaces and removing a lot of hardware from the desk. When I saw the icon interface, I realised it's more than an interface and mixer, all the functions are also enabled as control surface for DAWs. I got hopeful that I should be able to use this for both studio and workshop using the same large display screens to throw up all sorts of spectrums and analysis as well as route test signals out from the many analog outs on the icon. It has six outs, wouldn't that mean being able to test and measure up to active 3 way speakers? I am certain that, like a normal mixer, the digital mixer will use the knob on the top row for gain and the fader for post channel strip volume. Since it's a rotary encoder used there, it syncs with the knob in the DAW. The DAW should be able to display gain setting and amplitude and let you balance the pre and stereo mics and such and save them as presets. I am hoping to achieve similar potential as you but mostly pc and controller based
A mike calibrator like the one above its a really good investment. However don't get too obsessive about sub 1 dB acoustic measurements. Everything from a small change in the ambient temperature to barometic presure to a very small change in location can cause a significant change in measured level. Madness lies down that road. . . if you get better than 1 dB repeatability in free space day to day you are doing very well. Even the calibrators can change. The pistonphone seems the most stable since its based on mechanical displacement that does not change. The others use driver like transducers which do age and change.
My TASCAM digital recorder DR40X with in-built stereo mic serves as usb audio interface as well. Mic gain can be set by up/down pushbuttons and is shown in the display. Very handy!
Remove the original volume control 'pot' and replace it by a decent stepped attenuator.
Cheers,
E.
Yeah, I was measuring the resonances of a guitar body; one position flat on a bed surface, the other, hand held vertically in a chair. Forget getting anything similar in different locations within a room. It wasnt until I did both at the chair location that anything started to resemble one another.
So I got my microphone calibrator today, from ebay. Finding the battery door, I put in a 9V and it made (I was later to find) a 1kHz tone, getting louder with the 114 and 124 db settings - "That's encouraging, I thought".
Of course, whatever socket it has doesnt fit my microphone (Apex 220), so one slice of bicycle tube, backed with one slice of duct tape and I got a snug fit. Hopefully sealed good enough.
Using REW, and my Tascam US-122 setup (I have a Focusrite also) with the Calibrator set to 124 db, I manually adjusted the gain so that REW's Oscilloscope trace went close to, but not over, the displayed limits. There's an indicator on the US-122 going from green to red at this level. The display was a sine wave with no clipping - of course!
Then, using REW's SPLmeter, I selected "Use External Signal" in the calibration routine. With the Calibrator outputting 124 db, I simply typed "124" into the popup box. Then the db(c) reading became 124.
Switching to 114db on the Calibrator, I read 114.1, switching to 94, read 94.2. Not complaining for $20, shipped.
Of course, whatever socket it has doesnt fit my microphone (Apex 220), so one slice of bicycle tube, backed with one slice of duct tape and I got a snug fit. Hopefully sealed good enough.
Using REW, and my Tascam US-122 setup (I have a Focusrite also) with the Calibrator set to 124 db, I manually adjusted the gain so that REW's Oscilloscope trace went close to, but not over, the displayed limits. There's an indicator on the US-122 going from green to red at this level. The display was a sine wave with no clipping - of course!
Then, using REW's SPLmeter, I selected "Use External Signal" in the calibration routine. With the Calibrator outputting 124 db, I simply typed "124" into the popup box. Then the db(c) reading became 124.
Switching to 114db on the Calibrator, I read 114.1, switching to 94, read 94.2. Not complaining for $20, shipped.
A friend just wrote to me, telling me how my objectives could be met with a veroboard circuit costing a dollar or less.
He said that all I wanted to do is set the mic preamp gain pot to a fixed level time after time. I said yes, that's what I wanted. He said I didn't mind if I could not measure the driver SPL on an absolute dB scale. I said, that's right, I didn't mind. So he said I should build a small single-opamp oscillator circuit on a veroboard, and then keep two metal film resistors on its output as voltage divider to get a fixed voltage level as output. I could then feed this to my mic preamp and set the preamp gain to give me a specific reading every time.
I think this is true. Probably we didn't need a calibrator.
Of course the calibrator has the added bonus of letting me measure driver SPL on an absolute dB scale.
He said that all I wanted to do is set the mic preamp gain pot to a fixed level time after time. I said yes, that's what I wanted. He said I didn't mind if I could not measure the driver SPL on an absolute dB scale. I said, that's right, I didn't mind. So he said I should build a small single-opamp oscillator circuit on a veroboard, and then keep two metal film resistors on its output as voltage divider to get a fixed voltage level as output. I could then feed this to my mic preamp and set the preamp gain to give me a specific reading every time.
I think this is true. Probably we didn't need a calibrator.
Of course the calibrator has the added bonus of letting me measure driver SPL on an absolute dB scale.