Film-Tech Forum ARCHIVE: Iphone as an RTA or SPL meter

This is topic Iphone as an RTA or SPL meter in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Tristan Lane (Member # 1169) on 12-15-2008, 10:57 PM:

I was perusing the app store and ran across this app:
Link

I am seriously skeptical about the ability of the built in microphone as a measurement device, but it leaves one to think:

Why doesn't someone make a calibrated mic to use?

Then I noticed another sound measurement app, and this company claims that they will be offering a calibrated mic to offer true measurement. Their website doesn't have much info on the SPL app, but they carry a few others, including a phase checker. The AppStore is where the calibrated mic is mentioned.
Studio Six web page

It seems someone could port an FFT app or Analyzer app to run as well. With a reliable measurement mic, I'd be willing to invest in using my phone as a quick troubleshooting tool.

All of this isn't out of the question, since Ivie uses a PDA for the IE30 and IE33, it's just a question of the mic being used, and the "cleanliness" of the phone's input.

Posted by Mike Olpin (Member # 1115) on 12-16-2008, 12:26 PM:

I haven't used the apps you mentioned, but you should check these out:

I use SignalScope for iPhone - It's fairly solid for getting a quick snapshot of a room. I haven't compared it to other RTA meters in the same conditions, so I can't be certain of it's exact accuracy, but it's better than I originally imagined when I bought it. For 29 bucks it's hard to beat at it's price, and a great geeky toy. I've pulled it out to analyze the wave and envelope of airplanes, a foghorn, crowds, or whatever happens to be catching my ear. It's fun to have an RTA in your pocket! I don't think I would use it as reference to tune a room though.

But the real killer app is called SignalSuite and is only 10 bucks. It can generate all kinds of signals from white/pink noise, speaker pops, frequency sweeps - you name it. It can output 2 signals at once, separated into the iPhone's L/R output. It offers an amazing level of control over the signal too. I would highly recommend this app.

http://www.faberacoustical.com/products/iphone/

There is a video demonstrating both here:
http://www.faberacoustical.com/Downloads/movies/iphone/SignalSuite_Demo/index.php

Posted by Brad Miller (Member # 2) on 12-16-2008, 01:19 PM:

Hey Mike, any chance the next time one of the BL&S guys (or whomever) is coming through with an RTA you could do a comparison against the iphone app? I am curious as to how accurate it is and where the rolloffs occur.

Posted by Tristan Lane (Member # 1169) on 12-16-2008, 02:22 PM:

So a little more research finds that the Faber Acoustic app will allow you to measure from the mic input on the 1/8 jack of the phone. I'm going to test using an EMW mic with adapter, but since there is an issue with balanaced/unbal I'm not sure what to expect.

Mike, Does the RTA app have an option to use an external input device? Can you switch it over to the headset mic?

Posted by Mike Olpin (Member # 1115) on 12-16-2008, 02:37 PM:

As of right now, It only works via the headset input or the built in mic. You can use a camcorder A/V cable to access the "third tip" on the headset input, allowing you to connect something else to it, but it will be expecting a low level mic signal. Also, the first gen iPhone has a recessed headphone jack, which my cable didn't fit into. The headphone jack adapter I bought for it didn't pass along the third tip either. The A/V cable works well on my 3G iPhone though.

The latest iPhone firmware should allow for stereo line level input, but I haven't figured out how to do that yet.

Brad, I'll ask them next time they're here.

Posted by Mark Gulbrandsen (Member # 72) on 12-16-2008, 06:18 PM:

Actually for setting system levels it should work fine as long as it's calibrated against a known standard microphone or analyzer for level. For eq'ing a system... there are only two analyzers useful for that, the R-2 and D-2.

Mark

Posted by Joe Redifer (Member # 3) on 12-16-2008, 06:31 PM:

Is THX even still in business?

Posted by Steve Guttag (Member # 268) on 12-16-2008, 07:19 PM:

Yep...they'll certifiy ANYTHING. We actually have 4 theatres that we re-certify each year. We also have the R2 and D2 (which is not made by THX anyway)

Steve

Posted by Joe Redifer (Member # 3) on 12-16-2008, 11:14 PM:

Really? I thought those were the only two analyzers allowed to certify a THX house, at least initially. Plus, they're named after a Star Wars character, so clever.

Posted by Mark Gulbrandsen (Member # 72) on 12-16-2008, 11:22 PM:

They don't answer their phone... so most WOULD THINK they don't want any business or that they are out of business. Its pretty obvious they are operating on a shoestring as far as the theater end goes. One can assume the theater end IS NOT a money maker for them like certifying computer speakers, car stereos, or DVD's.

Also, their Technical Services Division's phone number has been temporarily disconnected!

Mark

Posted by Joe Redifer (Member # 3) on 12-16-2008, 11:50 PM:

Always appropriate:

THX trailer - Quicktime

THX trailer - Windows Media