my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Sound card for RTA (Page 2)

This topic comprises 2 pages: 1  2

Author Topic: Sound card for RTA Catalin Balaceanu Film Handler Posts: 36 From: Pascani, Iasi, Romania Registered: Mar 2006 posted 05-18-2008 09:27 AM                        quote: Tristan Lane I use SpectraRTA exclusively now in conjunction with a USL mmp-10 4 mic Maybe it's a bit off-topic, but does SpectraRTA have the X curve reference feature? I know that the latest version of TrueRTA has it. Catalin  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 05-18-2008 10:24 AM                     You can make it by yourself. Spectra has "overlay" curve files, just create some files with all the X curves you want and it will be overlayed on the RTA screen. I have many kind of overlay: X-500, bigger and smaller screens. Marco  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-18-2008 12:36 PM                     This is a case where the R2 or D2 really stomps over the other solutions... The R2 or D2 has calibration files for EACH microphone and they also NORMALIZE the response to mic 1. That is, Mic 1 sets the SPL reference and then the other three are raised/lowered in SPL to have the display not bounce around. The problem I see with the USL multiplexer on other analyzers is that at best there is one compensation file as the analyzer does not know at any one point in time which mic is active. They also do not normalize the display so the mic closest to the screen is shown louder than the one furthest from the screen. As such, a frequency anomolie nearest the screen will get more weighting than one furthest from the screen. This is not the case with the R2 or D2 due to the normalization feature. As to those that use microphone compensation files with your analyzers...who is making these files? That is, what is the basis for these files? Are the individual microphones being measured? If so, by whom and how valid is the measurement? How often do you have them rechecked? With the R2 or D2 system, there is a means to have the mics rechecked with a new offset file as often as desired (about once per year for us). BTW...I too love my Abacus scope attachement...it is the best analyzer I've ever seen in terms of display and ballistics. I still use it for A-chains and for quickie B-Chain checks. Steve  |  IP: Logged Tristan Lane Master Film Handler Posts: 444 From: Nampa, Idaho Registered: Feb 2002 posted 05-18-2008 01:49 PM                     Steve, Your remarks are in line with what I have found as well. If there was one problem with the USL plexer, it is that the measuring device is "dumb" as to what mic is being measured and at one time. You can actually see the response fluctuate when the plexer is cycling. In addition to this, there's always an issue with controlling noise gating. I only successfully got it to work once, and found it to be too big of a pain. SpectraRTA has functions for RT-60, but without a precise control of the pink noise from the software, times wouldn't be accurate enough. My way of dealing with the fluctuation between microphones was to tell the software to average for a given time, and then make adjustments based on overall response. Generally I would repeat this process two more times and take a final read. To set levels, I stop the plexer at mic 1 and set the channel gain accordingly. As far as mic compensation files, I've never used them for anything other than x-curve. I liked the way the R2 showed the response as flat on the display when in actuality, the response was in accordance with the curve. I mimicked this within SpectraRTA by adding 1DB of boost consecutively to each 1/3rd octave over 2k. Then when a proper curve was achieved, it would appear flat on the display. Unless you sent your mic off to TXH, or another similar lab for reference testing, I doubt you would gain anything other than a general figure of what the response of the mic was. And like you said: It only applies to one of the 4 mics. I still believe that the overall measurements taken by the USL system are going to be better than many of the single mic setups being used.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-18-2008 05:10 PM                     The only way I could see the USL system being notably better than a single calibrated mic is if you took the time to balance out the inputs each time you set up the system. That is, play pink noise and note the level in mic 1...then set the other three mics to match (EACH TIME YOU set up the system in each room). For the offset file, you could then send all four mics out for measurement...then create an average file that represents the average off all four mics since hopefully the analyzer under use is showing an average of the four mics (time sample is longer than it takes to sweep through all four mics). By in large, this is not what I see. I see most people just plunking the four mics down and tuning up. Well, without offset files, you are tuning the room to the mic's response, not for "flat"...and furthermore you are tuning primarily to the "loudest" mic. The USL mics are not necessarily the flattest things and neither are the R2 or D2...the key to them was having accurate offset files. Prior to the R2, the AKG C451 with an omni module seemed to be the defacto standard for measuring theatres. I know that AKG supplied a individual response curve for mine...including when I sent it back for repairs and it was pretty darn flat. That mic was many hundreds of dollars though. Steve  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 05-18-2008 07:20 PM                     Hi Steve R2 and D2 are the best RTA analyzer on the market, this is a fact. Said so, I use two channel soundcard (L + R) and have SPECTRA averages both channel in amplitude in real time. Both channels have its compensation file, made by a lab in Germany. I sent my mics to this lab, they provided a file with amplitude and phase compensation in TXT format, plus PDF graphs. For my needs it's enough. I agree with you that once (or IF) I'll need more, the next and unique step will be the D2. Thanks for the amplitude hint. I really never thought about it. Spectra, however, shows "algebraic average" of the amplitudes of the channels. The response curve should not change if one mic is higher in level than the other. But using the USL yes, you're right. Thanks Marco  |  IP: Logged Tristan Lane Master Film Handler Posts: 444 From: Nampa, Idaho Registered: Feb 2002 posted 05-18-2008 11:38 PM                     Steve, You may be right in that your method would provide the most accurate readings for each time you adjust, but the USL has proven to be fairly reliable. USL claims that each mic is calibrated at the factory, and that no compensation is needed to achieve desired results. Yes, the mics are not inherently flat, but overall gain on all mics can be perfect since the plexer has adjustments for each mic's gain. I used to be as skeptical of the USL kit, as my prior experience was strictly with an R2 or Ivie. Since I had doubts as to the accuracy of the new product, I decided to tune a room with it and then save the readings for future reference. I then set up an R2 in the same room, taking care to place the mics right next to the USL mics. I compared the readings of both spectra RTA and of the R2 software and they were very close (+/- 2db on a few frequencies). I even connected the USL plexer to an input on the R2 box and took a reading within R2 software and got similar readings. I'm certainly not denying that the R2 or D2 are a much more robust and accurate measuring tool, but I'm weary of single mic tuning, and prefer the USL over it.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 05-19-2008 06:18 AM                     Microphones cannot be "hardware calibrated". Every microphone has its response curve and it can be corrected only by software. USL device will not calibrate it since the software will see only one input. About the ability to adjust each input of the USL, is what Steve has said, but you should adjust each microphone's level for each screen. Regards Marco Edit: best reply was from EMU support. They can't say if the EMU 0404 suits my needs, the best thing is to test it from a dealer by myself and decide if it is good for me  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 05-19-2008 07:47 AM                     All of this has been discussed man many times before in these threads and I'm surprised the F-T police haven't slammed this thread in with some other one from 2002. Fact always was and still is. R-2 and D-2 are the most accurate standard analyzer for cinema. If you don't own one then you can't work to any sort of accurate standard period. The fact that the mics are normalized is but touching on what either of them are capable of. Personally on the offset files I have often wondereed just how accurate the R-2 and D-2 offset files are done... Since it is also done as a side by side comparison with a mic "standard" it may depend more on how the person who is doing them feels on any given day than anything else and its this part of the R-2/D-2measurement system that I always thought should be automated at the manufacturing end. Aside from this there is no other accurate enough analyzer in my book. Mark Mark  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.