Spektrum is a shareware program. You can freely distribute it (be sure to include this document, too) and try it out, but if you like it you should honor the shareware system by sending $5 to the author at the address below. Since cashing intenational cheques is very expensive, please send cash only.
Francesco Meschia
Via Baroncini, 4
14100 Asti
Italy
If you can't afford this, well... a nice postcard is much better than nothing at all!
I can also be reached via E-Mail for comments, suggestions, and bug reports. My Internet E-Mail address is:
fmeschia@freenet.hut.fi
• DISCLAIMER
As an independent software developer, I can make no warranties whatsoever on Spektrum. As far as I know, it is System 7 compatible and 32-bit clean; it shouldn't damage to your system, but use it at your own risk.
• VERSION HISTORY
2.0.1: minor fixes. Recompiled with the latest version of the compiler.
2.0 : first public version. Can record and play sounds.
1.1 : many bugs fixed.
1.0 : experimental version. Could only analyze previously recorded sounds.
• WHAT IS SPEKTRUM?
Did you ever see those nice hi-fi systems which display a histogram-type graph while playing music? If you did, you probably know that it's called a SPECTRUM ANALYZER, a piece of hardware which gives you information about the acoustic power distributed along the audio frequency domain (20 to 20,000 Hz), usually split into many channels.
Now, you know your Mac can play and record music and sounds: it's not like a hi-fi, but it's funny. And if you want to know more about the sounds you're recording, you should use Spektrum!
Spektrum can analyze any standard Mac sound file, showing you its acoustic power spectrum in 256 channels ranging from 40 to 11,000 Hz. You can measure the frequency and amplitude of every channel, and you can also record a sound "on the fly", if you have a microphone connected to your Mac.
Well, how could it be useful to you? Spektrum is more serious than you might think. You can use it to analyze your voice, and to study the difference between male and female voices. You can also study sound spectra from musical instruments (that was the reason for which Spektrum was created), discovering what's the difference between a classical guitar, an electric guitar, a piano and a violin, or between two instruments of the same kind (e.g., a cheap violin and a Stradivari). You could learn how your guitar distortion works, and in which way a tenore voice is different from a soprano voice.
“Omne tulit punctum,
qui miscuit utile dulci”
(Horace)
- and don't forget to send your contribution.
• HOW TO USE SPEKTRUM
When you start Spektrum, you will have to open an existing sound (only standard 22-KHz Mac sound files are supported) or record a new one: to do so, simply choose "Open..." or "New..." from the File menu. If you must record a new sound, please note that you must limit yourself to a maximum of six seconds of live recording: this is because every second of good quality audio takes about 23 Kb of your valuable RAM, so I thought 6 secs was a wise choice! You can have more than one sound open at a time, as long as they fit into your free memory: if you need more memory, you can always increase Spektrum's partition with the Finder.
After opening or recording a sound, Spektrum will open a window with two panes, the upper one showing the time evolution (wave) of the sound, and the lower one showing its spectrum. Please note that the spectrum isn't computed over the whole sample, but only over a small portion called the region of interest (ROI), which is highlighted in the upper pane. At first, the ROI is located at the very beginning of the sample, which will probably contain just noise, so that the spectrum won't look much pretty. Now, drag the ROI with your mouse to the portion of the sound you want to analyze, and Spektrum will compute and display its power spectrum. By examining consecutive points of the
sample, you can study the time-evolution of the sound in the frequency domain.
Since spectra are represented using a logarithmic scale, low frequencies are more spaced than higher ones. A linear interpolation is used to connect sampled points of the spectrum (which are identified by a vertical bar running down to the frequency axis), but please remember that this is only a guess! Because of the digital nature of the computed spectrum, you can't actually tell what's the power distribution between two computed points: you can just try to figure it out, and a linear interpolation is the simplest way to do so.
If you want to keep an interesting sound for later studies, you can save it in standard Mac format by choosing "Save As..." in the File menu. And, if you can't remember what it sounded like, you can play it back by double-clicking on the wave pane, or by choosing "Play All" (command-A) in the Edit menu.
• TECHNICAL NOTES
The sound spectrum is computed using a Fast Fourier Transform algorithm, applied over your sound sample windowed by a Hamming function. The upper limit of the frequency range is 11,128 Hz, and this is imposed by the sound hardware itself; the amplitude dynamic range is 48 dB, because of the 8-bit resolution of the standard Mac sound system.
