SoundInstructions
From MariachiWiki
Contents |
How to measure Speed of Sound
First, read carefully the manual that comes with the software oscilloscope. The manual that comes with the software explains how to use the software. If you don't have the most recent version download it from this address http://www.zeitnitz.de/Christian/Scope/Scope_en.html
Understanding sound cards
Typically a laptop has one headset output and a microphone input. Some of the larger footprint laptops, e.g., 17" may have microphone and line in inputs. The headset output is a stereo output and the microphone is a mono input. To measure the speed of sound you need a stereo input, because you will be using two microphones. On a desktop computer the stereo input is the LINE IN input. Most laptops don't have a line in input and therefore you will need to use an external USB audio adapter.
There are many different external USB audio adapter, as the one you have received during the workshop. If you don't have one, search the internet for a reasonably priced unit. Having an external sound card is also a good idea as if there is a problem, such as shortening the input or output, you won't damage the laptop sound card.
Jack
The mini-stereo jack (1/8" diameter) has three rings. For the headset and line in - from the tip to the body they are the Left channel, Right channel and Ground. By default when you play a MONO sound track you will hear the sound on your LEFT channel.
For the microphone input the rings are, from the tip to body, Signal, +5V and Ground. So be careful, the microphone input has a +5V.
Choosing the Input and Output
To choose the INPUT for the oscilloscope you must open the Sound and Audio utility in the control panel. Click on the Audio Tab and select the device you want to use as the INPUT, that would be the Recording device. Click on Volume for that device and select Line In as the input. click Apply and OK.
Playing the output sound
Download the wav file from here. You can use any software that plays wav files. Audacity plays the sound as well as Windows media player. There are many different choices here.
Adjusting the oscilloscope
Measuring the time difference
The OUTPUT is the device you will use to play the sound in the mini speaker. You can use the laptop output, or the USB audio output.
Testing the Oscilloscope
To test if the oscilloscope is properly connected, tap near the microphone to see any activity in the oscilloscope. If there is no activity, first check the input device in the control panel.
If there is no apparent signal, you could try Auto Adjust on the oscilloscope panel.
Alternatives
If you are not using the software oscilloscope, you can still do the measurement using alternative software. At this time we have only tested the measurement using Audacity.
- Audacity - To use Audacity, connect the USB audio card in the same way as for the oscilloscope. Select Line in as the input, and when you record make sure you choose stereo input. You will see two traces and able to measure the difference between the left and right channels. Audacity has a better resolution for time measurement than the oscilloscope sound card.
Random notes
References
- On line calculator for speed of sound taking into account Temperature, Pressure and Humidity http://www.sengpielaudio.com/calculator-airpressure.htm
