Chris Kalcov, a student of the Tonmeister course at the University of Surrey and Grace Zarczynska, a software developer from University of York have created a useful little app for calculating delays in multi-speaker live sound situations and for multi-mic recording setups.
Released under the brand name 3g Sounds, the app, called Sample Delay Calculator, is available on iPhone and costs £1.49$1.99, however an Android version is in development.
Here's more from the developers:
Press Release: We're very excited lo announce our first iOS app for iPhone, coming out on 30th August 2013. Useful for all live sound, classical recording and broadcast engineers, and even for sound installations. Currently available on the iPhone 3G, SGS, 4 and 5, with Android coming soon.
Why time align sound?
The propagation speed of electricity down a copper cable is virtually intinite, at two-thirds the speed of light. The speed of sound through air, conversely, is a lot slower, and is dependent on air temperature. Therefore, for two point sources of a coherent sound, wavefronts will arrive at different times at a specific point depending on the difference in distance between the two sources. This causes audible blurring of transients and comb filtering, or even a distinct echo in the instance where the time of arrival differences are greater than 50ms. This problem also effects recording, whereby microphones capturing a single source may have great distance variations between them, for example in orchestral recording. By delaying the spot mic on an instrument to the main array, the engineer can ensure that the sound will arrive time coherently when printed onto tape, thus improving the clarity ofthe mix.
Time aligning and sample-level digital delay is a luxury recently found with the introduction of DAWs and digital mixers. Before this, when sound was mixed on analog desks, there was nothing much the engineer could do to correct the alignment error. In recording applications, arguably, the subtle time of arrival differences captured by the microphones contributed to the Haas ettect, allowing more accurate aural localisation to the human ear when listening back in stereo. However, we were not able to overcome transient issues and the effects of comb filtering, and could only go by our ears. Many gigs and recordings still came out well thirty years ago though as we all know so always trust your ears!
How does the app work?
The Sample Delay Calculator is provided to give quick delay calculation and ease of mind for precision alignment of speaker systems to a single location, and time alignment of microphones, where accuracy is key. It works based on the simple Speed = Distance/Time equation, but fully expanded using the most accurate derivations to compensate for other imperfections including air temperature. It specifies the required delay in milliseconds and samples, which you can then input into your digital mixer, DAW or speaker management controller.
Please note that the app calculates the delay for direct sound, not diffuse such as those reflecting from walls and other surfaces. Therefore, you should always still trust your ears, as the Sample Delay Calculator is only theoretically accurate when used in a strictly free-field environment. However, it does mean you won't have to drag a calculator with you to your next gig, or go loosely by the "1ft=1ms" rule.