How A Shotgun Mic Works
The long tube with slots on the sides visually distinguishes the shotgun microphone from others. Designed to be more directional than conventional microphones, how does that long cylinder with notches increase the ratio of on-axis to off-axis sound?
In the 1950s Harry Olson (of RCA 44 mic fame) created a microphone system that used a series of parallel tubes to improve directionality. The operating principle is frequency cancellation by difference in timing. Any time you take the same signal, delay and recombine it, there is a cancellation. The greater the timing delay, the lower the frequency that is cancelled.
Below we see a simple illustration with only two tubes, one longer than the other. The sound arriving at a common mic element ON axis will have the same path length. In other words sound arrives at the element through both tubes at the same time. But at an angle the tube length delays sound through the longer tube. When they combine, there is a cancellation at a certain frequency. So the path length difference cancels some off-axis sound but the on-axis arrives intact. Olsen used a series of tubes to cancel a significant portion of the spectrum, which made his system more directional than it would have been otherwise.
The more tubes you have, the more off-axis frequencies you can cancel, the more directional the system. But at some point the tubes take up too much space to be practical. So the next big development was to use ONE tube with ports in the side. Each port behaves somewhat like a single tube, changing the timing of sound arriving off-axis. A barrel with many ports front to back can cancel many different frequencies. Given the historical development of shotgun microphones, we better understand why they are also known as Line Array (many tubes arrayed on a parallel line) and Interference Tube (many slots cancelling down a single tube) microphones.
How do different shotgun microphones sound? Listen to the Shotgun Mic Test at recordinghacks.com to hear microphones by Sennhesier, Neumann and Rode.
LIMITS
How long a tube is needed to cancel the entire audible spectrum? Elecro-Voice made the 7 foot long Model 643, designed to cancel as low as 700 Hz. I don’t know about you, but a 7 foot mic nicknamed “bazooka” isn’t something I’ll be carrying in my gig bag. So the truth of the matter is that shotgun mikes only improve directionality at high frequencies (unless impractically long). Thus low pitched Harley drive by noise will not tend to be suppressed by using a shotgun mic any more than by using an ordinary mic with the same first order polar pattern.
Combining sound with a delayed version to cancel a frequency is also known as Comb Filtering. The null frequency will be notched but it does not cancel all sound perfectly. While the series of frequency cuts produced by the slots in the tube is sure to improve the ratio of on-axis to off-axis sound, it may not sound very natural. To put it another way, there is often a sonic trade-off in quality for improved directionality with shotgun microphones. Shotgun mikes are sometimes described as sounding “phasey” off-axis because of the comb filtering.
Now that you know more about how a shotgun mic works you will be better able to decide when one might be appropriate to use versus trying another solution.
If you find this article Pinteresting:
Pinterest: Why, How and Implications
I’ve compiled bookmarks in browsers and kept lists of URLs to help keep track of good stuff I’ve found online. I’ve even posted indexes of such lists to share with others. Pinterest makes it easier for me to do all of these and to find valuable info quickly from other people. The metaphor is pretty simple: when you find something you like online, you “pin it” to a bulletin “board.” Because it’s graphically oriented you can quickly look through what’s been indexed.
I have figured out a few things that help me curate my collections. If you use Pinterest, or are thinking about it, maybe these will help you along.
1. When you first create your Pinterest account, designate your Facebook setting to “only me” so you don’t have to spam everyone with your initial pinning activity. Then you can deactivate feeding Pinterest to Facebook from the Settings menu.
2. The simplest way to pin something is using the “Pin It” button available for your bookmark toolbar. If you have an account, pulldown “About > Pin It Button” and scroll to the top of the Goodies list. Drag it to your bookmark toolbar. Whenever you see something you want to save or share, click it in the toolbar, select the image and type a brief description in the new window. Done.
3. If you want to pin a page but there are no images:
a. Go find an image somewhere else and pin it.
b. Edit the pin and paste the desired destination URL in the Link field.
4. If you include a number with a dollar in front of it in your description, the pic will be displayed with a banner showing that figure. If you use more than one dollar value, the last one gets bannered. You can see examples of this on my Audio Test Equipment board.
I’m using Pinterest as a “see also” for some of my articles. It’s an easy way to include related info from other sites and it’s so simple to keep a board updated. My Pinterest boards often point back to my site, for simplified indexing. Because Pinterest organizes information based on a picture, I’m motivated to include something that graphically represents what I’ve written on every post, making it easier for people “Pin It” and find it among other information on someone’s board.
Gamification
Libe Goad suggests game developers might consider enabling gamers to graphically collect, “their favorite products or uses from a brand or company to a shared virtual space, or perhaps their favorite scenes and characters from a film or television show.” Taking her idea a step further, what if gamers were allowed to collect favorite sounds and trigger them, replacing stock audio assets in a game? We’ve seen “play with your favorite song” as background music to the game. But curating and replacing sounds wouldn’t merely re-skin a game. This would let users design their own game audio mashup. Not a simple thing to implement, either by allowing your assets to be taken or getting the volume right for outside assets users import into your game. This kind of thing would probably work best in a game that has a sense of humor to it. It certainly takes the idea “interactive” to a new place.
Want to add this article to one of your Pinterest boards?
Headphone Comparison: Shure SRH 840 vs. Sony MDR-7506
Given the choice, I would prefer to listen on speakers rather than headphones. And while a mix should be checked on headphones, I don’t think mixing primarily on them is a good idea. My biases against them aside, there are times when headphones are useful, even essential. I bought a pair recently and thought my findings were worth sharing.
The Standard Bearer
The Sony MDR-7506 headphones are popular for audio production in Southern California. They are considered relatively flat and trustworthy for the price. I have found them to be a bit bright and a little weird on the low end. Then again, headphones generally sound harsh on top and strange on the bottom — the Sony’s seem better than most. One of the biggest problems I’ve had with them is poor isolation; outside noises are not very well blocked. In noisy environments I have to turn the headphones up louder to hear the signal, which fatigues me quicker and makes them seem more harsh.
The Challenger
In 2010 I watched a gear review by Ronan Chris Murphy where he had nice things to say about the Shure SRH 840 headphones (review starts at 1:51). Certainly the brand is known for durability and Ronan specifically mentioned how well they block noise, so I put them on my list. I couldn’t find an audio dealer that would let me demo headphones. I understand hygiene is a factor, but I wasn’t asking to wear them for hours and sweat in them, just listen for a few minutes. No one would let my try them. So while I wouldn’t buy a pair of speakers without listening to them first, that’s exactly what I did with the 840s. I just had to hope Ronan didn’t steer me wrong.
I was considering buying a second set of earpads to extend the life of the headphones, so I was pleasantly surprised that Shure included a replacement set in the box. Another bonus: the cable separates from the headphones. I’m not sure the 840 cable will last any longer than the 7506 integral cable, but at least this one will be simpler to replace if/when it does fail.
Head To Head Phones
It turns out I do prefer the 840s, primarily because they provide superior isolation. The trade off — to block outside noise closed headphones like the 840s also trap some sound inside. It’s like listening inside a sea shell, only less dramatic. All closed back headphones seem to have noticeable interior reflection and the 840s are no exception. These do a decent job of minimizing it, but by comparison the 7506s do not exhibit this problem. Interestingly the top end seemed similar. I trust the Sony headphones more after this experience. The bass seems to extend a bit lower with the Shure headphones, but not dramatically.
The list price for Sony 7506 headphones is about $70 lower than Shure. To be fair, these two models probably shouldn’t be considered same class. For example Sony offers the 7510 for a list of $150 and the 7520 for $500, both of which look like they would block out noise better than the 7506. It seems more likely that the Shure SRH 440 and Sony MDR-7506 would be an equitable face off. (My friend Jon Tidey, @theaudiogeek, noted about the SRH 440: “The plastic clicks and creaks and has been a problem for vocal tracking more than once.”)
Fair comparison or not, what I like about the 7506 is a realistic frequency response at a good price. The 840 sounds as good (or slightly better) with greater isolation, which has been useful to me. However I’m not convinced that the 840 seems $70 better. I really wish I’d had the opportunity to try the 7510 and similarly priced headphones by Sennheiser and Beyerdynamic.
If you’re in the market for a new set of headphones I hope this review will help. If you can assist others with your experience using headphones, please leave a comment. For more see my Pinterest board, a collection of quality Headphones, including price. See also Headphone Mecca, a site that recommends models by 3 categories in 6 different price ranges.
If you’d like to add this page to one of your Pinterest boards: Pin It
Better Media Production with Q-Dir for Windows
Collaborative media production usually means two things: several people sharing a large number of media assets, and a deep folder hierarchy to keep everything organized. Let’s say I’m editing voiceover recordings from someone else. I like to move from the source folder of the recording engineer’s files to my folder of edited soundfiles. Invariably there will be other locations for tracking documents, scripts, etc. This kind of workflow is useful for photography, video game production, film production and other kinds of media.
On a PC, getting all of the windows open to the appropriate folders can take time. And if you are switching back and forth between folder sets for different projects, the time spent managing windows increases. My co-worker D. Shinji Furuya got me hip to Q-Dir, a free quad explorer for the PC.
Click to enlarge
Launch Q-Dir and you’ve got 4 windows open. Once you click your way inside to the folders of assets, you can save your “Work Area” view settings. That means you can return to the same set of files/folders by simply opening your saved Work Area. This has been an enormous time saver for me. Switching back and forth between projects is a breeze. There are other features like filtering for quick access to the stuff you need.
The price is right; Q-Dir is free! Download here. Let me know what you think.
Check out more info like this on my Game Audio board.
Want to add this page to your Pinterest board about Game Audio, Film Sound, Asset Management, Audio Production or Voiceover? Pin It
When Is Good?
There are some great calendars for sharing your schedule. They can also make it easy to organize meetings if everyone you are inviting is member to the same calendar (Outlook, Google, etc.). But if some are not, scheduling can be complicated. And if your invitees don’t want their email addresses put into some calendar system (because they might get spammed later), you might think there are no considerate options.
Ah but there is hope: WhenIsGood.net is a simple little website with the power to help you find a good time for everyone to meet. No email addresses required! You start by filling in all of the times you want to be considered available. Then the site gives you some links:
1. A link that allows attendees to fill out their availability,
2. A link that shows results from everyone who’s filled it out, and
3. An edit page in case you need to change your availability.
You share the links with the folks you’re inviting — not the website — so no one has to sign up for anything or get spammed just to participate.
As people highlight their availability on your schedule, common times can be seen on the results page. It’s simple and effective. It works for anyone with a browser. I find it especially helpful when trying to schedule a large number of people. Now this site doesn’t guarantee it will find a time in everyone’s busy schedules. But if there is a good time for all the people who need to meet, WhenIsGood.net can help find it.
DIY Cable Tester
When I first started working in audio I built a lot of cables. I wanted them to be reliable so I needed a quick and accurate way to verify that my cables worked. I’ve seen some cool testers over the years, but none supported the combination of connectors I commonly used. So I decided to build my own. I purchased parts: plastic enclosure, bread board, five-way switch, four LEDs, four resistors, hardware for a nine volt battery, and a pair of all the connectors desired.
The connectors are, from left to right: quarter inch Tip-Ring-Sleeve, RCA (cinch), BNC, XLR along the top and bantam (TT) along the bottom.
Click any image to enlarge
Do you have a Pinterest board about audio test equipment, DIY projects or audio wiring? Pin this page
Curious how the tester is wired? Want to build your own? Here’s a schematic.
Conflict: ProTools and Spotlight Indexing
According to the Avid ProTools 10.0.1 update documentation dated Jan 18, 2012:
Spotlight indexing can interfere with long record passes (97151)
There are known incompatibilities with Spotlight indexing drives while recording audio. If you will be recording to a large number of tracks for over an hour, set all of your drives to private in the Mac OS X System Preferences to ensure maximum performance. Failure to do this may result in Pro Tools reporting an error and ending the record pass when Spotlight indexes the drives.
It took me a few minutes to figure out how to do this, so let me save you the time. Screen shots are from Lion.
In System Preferences, you should see Spotlight toward the right of the top row.
In the Spotlight preference area, click the Privacy tab.
Click the “+” on the lower left and choose a record drive.
The OS will display this warning. Click OK.
You will see the selected drive on the Privacy list. Continue this process with any/all record drives.
Please note that you wouldn’t want to actually prevent indexing of your system drive as shown here; this is merely for example. You wouldn’t want to record to your system drive either.
See the full Avid document here-
akmedia.digidesign.com/support/docs/Pro_Tools_v10_0_1_ReadMe_Mac_75091.pdf
@kylepsnyder made an excellent point about the example shown above: do not disable indexing for the system drive. He also advised that Spotlight indexing, Time Machine and much more can be managed using Cocktail. Cost: $19.
If you want more tips for making your Mac great for audio work, be sure to read OSX Optimization for Audio by Jon Tidey (@theaudiogeek). It is a great companion article to this one whether you use ProTools or something else.
Side note: in my opinion Finder and Spotlight have become less and less useful for finding files. Allow me to recommend EasyFind instead. It’s great and it’s free.
See also: ProTools + H.264 video = Problem
Portable Audio Test Equipment
If you’re like me, you end up in situations where you need to trouble-shoot, verify or calibrate your audio stuff. If you have access to a tech shop with expensive scopes and waveform generators — life is great. If not, your most cost effective solution may be something portable. Here’s a list of portable test equipment that costs under $1,000.
If you are aware of any other tools that should be added, please let me know.
Portable Audio Tone Generators
For Under $1k
Horita PT3
Portable Tone Generator
www.horita.com/video.htm#PT3
Creates two tones (1k Hz & 10k Hz) via balanced or unbalanced output and has selectable line levels (+8dBu, +4dBu, -10dBV, +5dBV, -50dBu/V). Low battery indicator. 9 VDC.
List: $189, Retail: $155
Horita BSG-50
Video Sync Generator with Tone
www.horita.com/video.htm#Blackburst,_Sync,_Audio_Tone_Generators
Multiple output (BNC) video sync generator that also produces a 1k Hz tone at 0dBu via unbalanced RCA output.
Retail: $325 – 440