“Real knowledge is to know the extent of one’s ignorance.”
Confucius

One of the sincere joys of teaching at the Cleveland Institute of Music and Peabody Conservatory of Music as well as presentations at seminars and technical meetings is that I always learn something from my students or someone in the audience. April was full of teaching and learning experiences.

CIM students visited Audio Technia outside of Cleveland, Ohio to experiment with making anechoic recordings.

The Peabody Masters Class is now finalizing the design and nearing renovation of their new control room.

Our home theater research was presented at Home Theater Now at the New York Hilton. Two 90 minute presentations were given: Acoustic Distortion in Home Theaters and Desktop Auralization of Home Theaters. You can download abstracts of these presentations in RPG®’s new Acoustics Library.

Visiting the New York Hilton is always nostalgic for me in that it was there that I presented my first acoustics paper in 1983. This was the same conference that the CD was introduced!! Things were a bit different though as the Hilton is renovating and the lobby bar, the site of countless “seminars”, was missing.

Ever since we began representing the CATT Acoustics room prediction and auralization program, I have been intrigued by its ability as a powerful design tool and also its teaching and learning potential. While the body of experience using room prediction has been in larger performance spaces, we are attempting to bring some of this experience to the smaller rooms, including recording studios and home theaters. One of the helpful features in CATT Acoustics is the ability to create a room shape using a simple structured programming language. Our goal is to program a range of typical room shapes and then by adjusting the values of descriptive variables like length, width, height, etc. you can tailor the room to a specific project. This feature saves a lot of time. Since home theater is the fastest growing segment of our markets, we collaborated with Bengt-Inge Dalenback, creator of CATT Acoustics, to program two generalized home theater designs, including soffits, variable corner angles, adjustable wall areas, etc. One for the 5.1 THX dipole surround format and another for the ITU matching monopole surround format. To experiment with these, just download the CATT Acoustics program and the HT5.1THX and HT5.1ITU files. In CATT Acoustics, select the master.geo and implement.geo in the input folder and select the appropriate source and receiver location files. Select General Settings from the Prediction Module. Then select the input folder that contains the concept home theater files for HT5.1THX or HT5.1ITU. For example, for the HT5.1THX these include master.geo, implement.geo, and the source (thx_src.loc ) and receiver (rec.loc) files. Also in General Settings, select Sources and choose A0 thru A5; these are the five loudspeakers. In the Prediction Module, choose Geometry View/Check and select Save and Run. You should see a 3D drawing of the home theater with the five speakers A0-A4 and listening position 01. Select Geo-file in the Prediction Module and examine the room design. Change the Global room length "L" from 7 m to 14 m and save the file. Then hit Save and Run again. Notice how the room changes size automatically.

Visit To Audio Technia

The library of anechoic sound sources needed for auralization is rather limited. At CIM we have undertaken research to explore approaches to making anechoic recordings. Ideally, a full sphere directivity response is needed for each source. To begin exploring the variables, we developed a 10 channel recording approach using the Audio Technica ATM35 miniature condenser microphone. 8 of the microphones are at the corners of a rectangule 80" high x 74" long x 51" wide equidistant from the musician; 4 (hanging) above and 4 below (on the wire mesh floor). Two additional microphones are placed above and below the instrument. In the case of the violin and cello, we followed the advice of Norman Pickering and placed each microphone perpendicular to the top and bottom radiating surfaces of the instrument. In addition to the digital recordings, SIA Smaart was used to provide an absolute calibration of a pink noise source recorded by the front upper microphone as a calibration standard for future recordings, using the same mic preamps and reference loudspeaker.

The 8 microphone signals from the corners of the rectangle were recorded on an ADAT and the two microphones above and below the instrument were recorded on a 2 channel DAT recorder. The students are in the process of synchronizing the two channel DAT files with the 8 channel recording and converting to WAV files. They will then auralize the sound recorded by each microphone and audition the timbre changes associated with the different observation positions.

Any of this information is available to all interested parties. Since this is an ongoing research program, we would appreciate any suggestions other researchers may have.

RPG® and CIM would like to thank Audio Technica for their hospitality in allowing us to use the anechoic facility. A special thanks to Ms. Jackie Green for her time and support.