Monthly Archives: February 2014

Assignment 05 Record and Compare

Practical Experiment
Description: For this assignment you are expected to perform a set of small experiments as explained below. Your goals include evaluating qualitative differences between different microphones and different microphone positions.

The experiments on this assignment can be performed in studio F,  or your your home studio.  You will need to make sound on an instrument, voice or with a loudspeaker,  so try to book a time when making noise is ok.

You will new two microphones and necessary equipment (mixer, audio interface, etc) to get sound into your preferred audio recording app.  Please make sure that each microphone is recording into a separate audio channel.

If you do not have access to a musician/instrument.  Consider recording yourself singing with a microphone 10 to 20cm from your face and then play back the record into a loud speaker, and perform the rest of the experiments treating the loudspeaker as an instrument.

Record a short musical phrase (same phrase, same performance qualities) with various microphone positions:
1. Both close, on axis (microphone pointed at the instrument)
2. Both close, off axis (microphone not pointed at instrument)
3. One far, one close on axis
4. The other far, the other close on axis
5. Both far on axis
6. Both far off axis

For the report:
Post photos of your microphone placements, and recordings of each of the combinations.
How do the different microphones sound different from each other, if at all? How do each of the positions sound? How does the sound change when the microphone is on or off axis? How does the sound level change? How do the frequencies of the instrument change? How does the sound change with distance?

Assignment 04 Mixer IO Proof

This assignment is meant to quantify, and through that, hopefully simplify some of the challenges of working with mixers, and other audio input/output technology. Those with significant experience using mixers should replace this assignment with an alternate experience.

Tools needed:
A stand alone mixer (analog or digital) or a software mixer with an audio interface (which we will refer to as a mixer).
Means to generate and analyze test signals digitally.
(link)Suggested tools for testing at NYU

Test signal specifics:
All test signals should be generated at -20dB inside the software
Sine waves of variable frequencies and durations
Pink noise waves of variable duration
White noise waves of variable duration

The signal generating device must connect to the input of the mixer.
The mixer then must connect to the input of the signal analyzing device.

Pass a 1kHz sine wave test signal through the mixer with minimal distortion.
Pass the white noise through the mixer, observe the analysis.
Pass the pink noise through the mixer, observe the analysis.
Return to the white noise signal, this time apply equalization to produce an analysis signal that looks like the pink noise.

How many controls, gain-stages, switches, etc are between the signal going into your mixing and coming back out of the main output or control room output?
Describe/document how you were able to manipulate the sound using equalization.
Discuss the value of passing signals without distortion and how the controls of the mixer may be useful for you when producing recorded music.

Report due as blog post before our next meeting.
Use comment field below to link your report.

Assignment 03 Frequency vs Direction

This assignment is meant to help explore a some of the physical aspects of sound propagation in an echoic environment which dramatically affect recording quality.

Specifically we will focus on how frequency relates to directionality of sounds and how position in the room may alter the balance of timbres in a recording.

Tools needed:
Means to play test signals in a room at levels between 60 and 90 dB SPL, while being able to move/rotate the loudspeaker.
An SPL meter or SPL metering app for your mobile computing device.
Ear plugs (your ears are not needed as much for this experiment).
Test signal specifics:
All test signals should be generated at -20dB inside the software
Sine waves of variable frequencies
Pink noise waves o
filtered pink noise which passes only frequencies below 250 Hz
White noise waves of variable duration
Filtered white noise with passes only frequencies above 2000 Hz
Play a 1kHz sine wave through your loudspeakers such that you get an SPL meter reading in the 65-75 dB SPL range when 1 meter (~3 feet) from the loudspeaker.    Once you have established that you have control of the sound system and SPL meter, you may begin the experiments.  Do not exceed SPL levels above 85 dB SPL, especially with the filtered white noise.


Measure 5 or more non-harmonically related sine waves (spread between 100 Hz and 8kHz) and the 4 noise signals at several increments, rotating the loudspeaker in place in 15º or 30º for example.  Take no more than 10 seconds per measurement.

Repeat the above for the 4 noise signals, but this time rotate the SPL meter instead.

Using only the unfiltered noise signals,  measure the levels of the signals at 0.5 meters, 1 meter, 2 meters and if space allows, 4 meters.

Plot the results of your experiments
Analyze and discuss these results, especially think about your results in the context of the reading.
From these measurements, how might you expect recordings to differ with distance and orientation of the microphone?
How might you quickly test your expectations using your voice and a mobile computing device?

Report due as blog post before our next meeting.
Use comment field below to link your report.

Assignment 02 Amplitude vs Loudness

Goal:  Establish a clear understanding of how loudness can differ from amplitude.

Options:  See the exercises in the Moylan text at the end of chapter 13.  Complete the first exercise (13-1) and report your results, with your own analysis or complete the experiment below and report your results.

Experiment Description:
For this assignment you will need a program which can play pre-recorded or synthesized audio signals, at least one loudspeaker and an SPL meter.  iPhone and Android SPL apps will work fine for this.  If you are on campus you can checkout one of the SPL meters from the studio monitor.  You will need approximately 30 minutes to perform the experiments once your equipment and software are configured.

Specific Tools (if using NYU studios):
Work in groups of 2 or 3 if using the studios
Studio Computer, Laptop or mobile computing device.
Synthesis software (android app,  iphone app,  laptop app) or audio playback software.
Powered speakers (the JBL eons work great, they are in the “tech closet”).
Power cables for the speaker, plus maybe an extension cord.
audio cables to connect the laptop to the speaker audio inputs.
It may take you a few tries to get the right cables, give your self a few minutes for this process.

Sound signals needed:
100Hz sine wave at -20dB (8 seconds)
250Hz sine wave at -20dB (8 seconds)
500Hz sine wave at -20dB (8 seconds)
1kHz sine wave at -20dB (8 seconds)
1kHz sine wave at -20dB on sustaining, or looped
2kHz sine wave at -20dB (8 seconds)
4kHz sine wave at -20dB (8 seconds)
6kHz sine wave at -20dB (8 seconds)
8kHz sine wave at -20dB (8 seconds)

pink noise signal at -20dB (8 seconds)

white noise signal at -20dB (8 seconds)

System calibration:
Play the 1kHz sine wave into the sound system and adjust the levels until you get an SPL reading between 70 and 75 dB SPL on the meter or metering app.

Experiments: Play each of the test signals.  Then play the short 1kHz tone against each of the other test signals by alternating (1kHz signal,  then another test signal).  Note how each one sounds in terms of perceived volume or loudness.    Check your SPL meter reading with each signal to see if the levels actually change at all due to the sound system you are using or the acoustics of the space you are using for this experiment.  Finally consider adjusting the level of each of the test signals until is sounds as though its the same level as the 1kHz sine wave.  If you do this, be sure to record the SPL readings for each of the different sounds.

Analysis:  Discuss wow the sounds compared to the 1kHz sine wave.   Were some sounds more or less pleasant than others?    Plot any measurements as a bar-graph, line graph or chart.

Reports are due as blog posts online before our next meeting. Please put the links to your posts as comments at the bottom of this assignment.