Digital Audio Processing - Assignment 2 - Microphone Etude PDF

Preview

Summary

REPORT - 75% first class - The main purpose of the assignment was to compare different microphone techniques and examine the recordings. But since this was done already in an analogous assignment during the first year, the purpose of current assignment was somewhat changed. The students decided to f...

Description

Svetoslav Chemishev

Student ID: 12041769

Digital Recording Techniques Report for Assignment 2 “Microphone Etude”

Introduction The main purpose of the assignment was to compare different microphone techniques and examine the recordings. But since this was done already in an analogous assignment during the first year, the purpose of current assignment was somewhat changed. The students decided to figure out a new way for recording with multiple microphones. The fundamental aim was to be able to do a recording with as many microphones as possible, without changing the position, for a relatively short time, in other words ‘mass production’, because in a real studio situation, time is valuable. Moreover, in order to compare all of the recordings fast and easy, a software was developed, which would be probably represented it to the public.

Equipment Microphones: - Audio Technica 2050 (Omni) - Audio Technica 4033 (Cardioid) - Coles 4038 Ribbon Mic (Figure 8) - AKG C414 (Cardioid) - Gefell M930 (Cardioid) - Rode NT1-A (Cardioid) - Rode NT5 (Cardioid) - Royer R-121 (Figure 8) - Shure SM7B (Cardioid) - Shure SM57 (Cardioid) Other: - Audio Interface (Roland Octa-Capture UA1010) - Microphone Stands - Cubase 7.5 - Acoustic Guitar (Steal) - XLR leads - Collapsible Tent

Session 1 – Building and testing the Tent After discussing many different ways to achieve the intention, the students took a creative decision, to build a three-dimensional plastic pipe tent. That tent would allow them to keep the absolute same positions, so different microphones could be exchanged and recorded. Figure 1 demonstrates how the tent works.

Figure 1: Keith Holmes inside the tent In order to keep the same position of the performer, his legs, the chair’s legs and the guitar were taped. The current version of the tent allowed to put just 5 microphones at the same time. The techniques applied were: - ears’ height (left shoulder) towards the middle of the fret board - towards the 12th fret - 7 inches down/back from the 12th fret (close to the sound hole) - towards the bridge - towards the bridge (ears’ height, right shoulder) The first five microphones were positioned, then five rope strings with little metal plates at the end were hang on top of the exactly same positions as the microphones. After the metal plates were set accordingly, they became the reference points for the microphones. Thus, whenever microphones had to be exchanged from one position to another it was easy and fast to do so and get them in the same positions.

The process of building the tent was accompanied with a number of unpredicted issues. In order to be able to do get it done in the cheapest and most effective possible way, different sort of materials were considered and researched. In the early stages, the students tried to use some wooden and metal materials because the tent was not the most stable. However, they managed to build it entirely from and only with collapsible plastic pipes. Every single tent’s piece was properly labeled, so it could be built faster when needed. Also, the tent is absolutely portable and light. It is universal because it can be used for any sort of musical instruments such as drum kits, acoustic pianos, brass and so forth. The recordings were done in the box using a laptop and Cubase v7.5, which was connected to an external audio card Roland Octa-Capture. The group had took the decision to use the external audio interface with 8 inputs, instead of the mixing desk, because it was times faster and easier to set the levels, the files went straight into the hard drive, and to communicate in the live room. The soundcard has an ‘auto-sensing’ feature, which sets the gain of the microphone pre-amps, and in this case the students avoided setting up the levels of them manually. The programmed software’s objective was to allow the user to compare different microphones both quickly and efficiently. Besides that, the user can choose between a variety of instruments and microphone parameters to test a specific occasion. For example, see Figure 2 and Figure 3.

Figure 2: An acoustic guitar has been selected and 10 microphones have been loaded in at the same position

Figure 3: Demonstration of comparing different microphones at the same position (Note that distinctive polar patterns can be also selected if recorded)

Session 2 – Recording For the second session, multiple percussions were recorded using more ordinary way, which was to set up all the microphones as near as possible and record at the same time. It was done on two takes, with 6-7 microphones each, because it was not appropriate to put all the 13 microphones at the same location. This can be seen on Figure 4 and Figure 5.

Figure 4: A set of 6 microphones pointed towards the same direction

Figure 5: A set of 7 microphones directed to the same point The percussions recorded were: 1. 2. 3. 4. 5. 6. 7.

Jingle Bells Triangle Shakers Claps Agogo Twirling Pipe Mbira

The individual images of the instruments are located in Appendix B (CD). The Mbira and The Twirling Pipe are different type of instruments, but the students decided to use them, since the goal for the session was not to record a specific instrument type or group, but to capture the sound sources and test the microphones in a an unique way. Regarding the positioning, the microphones were set at about head height pointing down at a small angle and the instruments were performed at various spots at predefined distances. Jingle Bells were recorded at 50cm and 165cm away from the microphones at about shoulder height.

Recording procedure and post processing The group had to invent a practical and efficient system to organize everything. Two takes for each instrument were recorded at 24 bit 44.1 kHz. Firstly the students had to choose the best takes. The second take was considered as the better one, since the performer is being more concentrated. After that, all files’ lengths were quantized to end at the same time, of course different for each instrument, and the unnecessary silence was cut and the total duration shortened not to use excessive hard disk space. Next, everything was renamed according to the naming scheme used by the software. Finally all files were normalized at – 3dB to even out the loudness differences to make the comparison process more fair and accurate. Through using the offline processing method in Cubase all files were processed and bounced simultaneously in one click. This was a very important finding as exporting individual files one by one will be a lot time consuming.

Conclusion For the experiment were used the three main types of microphones, and tried a variety of polar patterns ranging from figure 8 to wide cardioid. Each microphone family has specific characteristics and the microphones, within the particular family does not vary that much. For instance, two condenser mics are used in exactly the same positions the difference in the frequency spectrum relatively are insignificant. However, sometimes there is an audible difference, due to the electronic components of each microphone, which can be heard in Appendix A. For the second session there were some disadvantages as well. It was impossible to place the microphones as accurate as the first session with the strings.

References Owsinski, Bobbby (2005) The Recording Engineers Handbook, Artist Pro Publishing, US http://www.uaudio.com/ (no date) (Accessed: 19 February 2014)

Bibliography Owsinski, Bobbby (2005) The Recording Engineers Handbook, Artist Pro Publishing, US Owsinski, Bobby. (2006) The Mixing Engineer’s Handbook: Second Edition. US: Thomson Course Technology PTR. Rumsey, Francis and McCormick, Tim (2009) Sound and Recording, 6th. Edition, Focal Press, Oxford, U.K...