This is a view ofthe Real Time Generator/Analyzer Screen
The audio is a singlesinewave Tone, at 550 Hz
The Tone is comingout of the speakers attached to the sound card
The Analyzer inputis the MIC input
Notice the peakat 550 Hz, with an apparent roll-off
The roll-off is dueto the bandwidth of the Analyzer
The Hz scale (Horizontal)has been widened (user defined)
to show that evenat about 50 Hz on either side of 550 Hz
the signal shownis about 40 db down from the peak.

This is a singletone, but the waveform is a TRIANGLE.
Notice the harmonicsappearing at 3, 5, 7, 9 ... times the base 1 kHz

Speakers are some inexpensive MS 691 Multi-Media 2' speakers Microphone is a Labtec AM-242 plastic boom mic This is a pair of tones. The Left speaker is about 6 inches from the mic and the Right speaker is about 1 inch from the mic Notice the relative amplitude of the two tones, showing the lower amplitude. Audio Test Software Key Features and Benefits:($7499) 1. Distortion free stimulus even the equalized stimulus. Unlimited channels acquisition and processing. Testing equipment manufactured by Dayton Audio is accurate, fast, and much more affordable than many other top solutions on the market today. Easy-to-use hardware integrates seamlessly with user-friendly software to provide easy measurements.

The left side ofthe program is generating audio which is being played
into a cheap setof speakers, using max audio volume and midrange
wav level, and midrangetreble and bass. This audio then goes into
an inexpensive microphonewith 20 db gain set, maximum level
One user noted thatthis spectrum plot looks more like a square wave
than a triangle,so we are assuming that the speaker, microphone and
settings used havedistorted the triangle into more of a square wave

The sound card mixersettings are obviously important
and the characteristicsof the output and input devices
are also going toaffect the measurements.

Sound card is a CreativeLabs Sound Blaster Live Value card
Speakers are someinexpensive MS 691 Multi-Media 2' speakers
Microphone is aLabtec AM-242 plastic boom mic

This is a pairof tones. The Left speaker is about 6 inches from the mic
and the Right speakeris about 1 inch from the mic
Notice the relativeamplitude of the two tones, showing the lower amplitude
of the 550 Hz tone,which could be due to (1) the distance of the speaker from the MIC
and/or (2) the frequencyresponse of the speaker/mic combination

This is a sweeptone from 100 Hz to 1000 Hz, and the frequency response of the speaker/mic
system on my computer.Notice the ramp up to about 175 Hz, a roll-off, then
a steady rise toabout 370 Hz, then a roll-off to -20 db from 550 Hz to 1000 Hz

Note: In this mode,the Tone Generator and Spectrum Analyzer are 'Tracking'
This is useful fortesting frequency response characteristics

This is a spectrogramof some piano music called
'TheEntertainer'
--
Here's what you'reseeing in the spectrogram:
The horizontal axisis time, the display is 'sliding' to the left over time.
On the verticalaxis is 'Energy' at the frequencies indicated
--
Notice the energycomes on the 'beats' in the music
and you can seethe notes played are repeated
Listen to the clip(link above) and look at the spectrogram
You'll get an ideaof what this display means

Create your own audio measurement systemstarting with TrueRTA software and your Windows PC. Then add a measurement microphone and USB interface and you have a full audio/acoustic test setup. Start with the free level 1 edition which provides a 1 octave spectrum analyzer, a dual trace oscilloscope and a signal generator. Level 1 never expires. Once you get to see the power of the software and how easily you become productive with it you will want to upgrade to a higher level with greater resolution. More...

Brent Butterworth writing for Sound and Vision Magazine, Jan 2011 :

'While lots of audio measurement software applications exist for the PC, the one that seems to have captured the hearts of engineers and enthusiasts is TrueRTA, available at trueaudio.com. Most speaker engineers I know keep a copy on their computers.'

Paul writes:

Speaker Testing Software Review

As an experienced electronic musician holding degrees in music and physics I have a lot of frequency analyzers at my disposal. TrueRTA is simply the best! It is feature rich and simple to use. The display is the most readable of any analyzer I have used. I always have it running when I am working on my music or recording and processing LP records. Kudos to the True Audio team.

Speaker Testing Software Reviews