About

The Analysis & Resynthesis Sound Spectrograph (formerly known as the Analysis & Reconstruction Sound Engine), or ARSS, is a program that analyses a sound file into a spectrogram and is able to synthesise this spectrogram, or any other user-created image, back into a sound.

News

May 30th, 2008 : The ARSS 0.2.3 released. Changes since version 0.2.2 :

• Fixed the logarithmic base system so that it produces the expected results when using a different base than 2
• Implemented linear frequency scaling
• Fixed the volume of noise bands in noise synthesis, although it may not be perfect and may be way off for logarithmic bases other than 2 and linear frequency scale
• Implemented bounds checking when reading and writing in the lower and upper frequencies
• Fixed the brightness setting input which would only take integer values
• Added a bit more information on the progress display line

Knows bugs as of version 0.2.3 :

• Clicks may appear when using noise synthesis on Unix systems (since version 0.2)
• Drag-and-drop in Windows will change the working directory to c:\windows\system32

May 9th, 2008 : The ARSS 0.2.2 released. Changed the formula used in the filtering function which reduces the visible time domain ripples which can mainly be seen on the lower part of spectrograms, hence increasing the quality of produced spectrograms.

May 5th, 2008 : The ARSS version 0.2 (final version) has just been released. It's the first feature-complete version since 0.1, which means noise synthesis is back in a rewritten and faster form, although not yet as fast as I'm working to make it. Here's a list of significant changes since the previous release :

• Noise synthesis has been re-implemented
• Full command-line support, meaning the ARSS can now be scripted, that you get define settings you couldn't directly modify before, but also that front-ends can easily be made for it
• Major reorganisation in the non-DSP code into easing the re-use of functions and the implementation of image/sound I/O functions by third-party developers
• Improved various aspects of IO functions, mainly regarding and few bugs and PowerPC compatibility
• Added brightness correction, a parameter similar to gamma correction. Makes spectrograms brighter, which allows for a better visibility when editing a spectrogram but also better sounding results

I would also enjoy it very much if a Mac OS X user could send me a statically linked Universal binary of the latest version of the ARSS, using something like 'gcc *.c -o arss -arch i386 -arch ppc -static -lm -lfftw3 -O2', as it would save the trouble to every other Mac OS X user of having to compile themselves.

Technical Description

The ARSS consists in two main parts, a spectrograph with a base-2 logarithmic frequency scale, and a spectrogram synthesiser.

Unlike most spectrographs which are based on STFTs (which perform the analysis by cutting the signal into small time slices to analyse these slices in the frequency domain), the ARSS is based on a filter bank followed by envelope detection, which means that the signal is cut into small frequency-domain slices, and then analysed in the time domain, in a manner quite similar to how analog spectrographs do.

The filter bank is, as of now, made up with overlapping logarithmic-scale frequency-domain Hann windows. Once the original signal is filtered with the filter bank, each resulting signal is sent to envelope detection. The technique used for envelope detection consists in obtaining the magnitude of the analytic signal. The resulting envelope for each frequency band makes the horizontal lines of the image representing the spectrogram. The amplitude of the envelopes translate linearly into intensity in the image.

The spectrogram synthesiser is based on modulation using horizontal lines of the image as envelopes. Each horizontal line is upsampled to the sampling rate of the desired final signal's sampling rate, and is then modulated with, depending on the synthesis mode chosen by the user, sines matching to the central frequency each horizontal line represents, or noise filtered through the filter bank.