Audacity

A ouple of very tidy tricks for using Audacity in AVS projects…

AudioStrobe

Use the Audacity Bandpass Filter to extract a piece of an audio track that contains the primary beat (usually a bass beat – below 1kHz typically) and then Pitch Shift it to around 19.2kHz. That will provide an effective AudioStrobe track. This will suffice if you are happy with the stereo variation at that bandwidth as a full expression in light, otherwise you can reduce the initial 19.2k selection to mono and save it as one track of AS, then reopen the original file and repeat for the second AS track (red/green).

Entrainment

The Tremolo Filter allows you to add amplitude modulation (entrainment) to any audio file or part thereof. The filter can be applied to selected segments of the file using the usual selection of waveforms. An audio track so modified can be mixed with a 19.2k track as prepared above to make a full AVS session.

Audacity (http://audacity.sourceforge.net/) is an open source program which I highly recommend.

If you would like more specific instructions, let me know via comments.

Cheers,
Craig

Further detail as promised…

Open your audio file in Audacity (File/Open). Assuming the audio file is stereo you can then decide whether you want to use the the two channels for red/green or if you want create the two AudioStrobe channels from different audio files.

If you want to use different files then you can merge the two channels into one (Tracks/Stereo to Mono) or delete one track (click dropdown arrow alongside track name – Split Stereo to Mono then X whichever track you don’t want to use). You can then import another audio file (File/Import/Audio) which you can make mono or split as before. You’re aiming to have two tracks which will map to red/green.

If you want to process the two tracks together you can use the Make Stereo Track option of the dropdown, otherwise you can use the Left Channel and Right Channel options and select the channels independently for processing.

It’s useful at this point to use the Analyze/Plot Spectrum to see how the frequencies are distributed – you’ll repeat this at each stage to ensure the right things are happening.

Click in the area displaying the audio tracks and use Ctrl-A to select all. Both channels will be selected – if you want to process left/right independently you will need to manually select each track – click/hold/sweep.

Now you use Effect/High Pass Filter to remove all frequencies above the beat you’re wanting to use. This may be a bit of trial and error – try 24dB rollofff, 500Hz cutooff for a start. Replot the spectrum – you’ll see that there’s now a gap at the left with a fairly steep rise.

Repeat using Effect/Low Pass Filter, using 48dB and 600Hz – again trial and error will apply according to the music you’re working with. Replot and you’ll see a single steep spike.

Repeatedly use Effect/Change Pitch 400% and then replot until the main spike is centred on 19000Hz (AudioStrobe uses 19.2kHz to trigger the lights). This may take some trial and error with the percentage – depending on the content of the audio and the starting frequency you filtered earlier. You can start testing with your AudioStrobe device at each step from here.

To finish the track use Effect/High Pass filter to remove everything below 18kHz (Rolloff 48dB/Cutoff 18000Hz). Repeated application of the filter will result in a steeper cutoff. Replot the spectrum and refilter until you’re happy with the rolloff. You can use the Low Pass Filter (48dB/19500Hz) to clean up the high end. Effect/Amplify can be used to adjust the brightness of the AudioStrobe display.

Finally, Import the original audio file so that you have the filtered/pitch shifted AudioStrobe track(s) and the music. You can also export just the AudioStrobe content for import as a sound file in Neuroprogrammer or Mind Workstation.

Effect/Tremelo can be applied here if you want to add an entrainment effect to the audio. You can also use Tracks/Add New and then Generate/Tone to create binaural beats(split into left/right with the tone frequency for each side being different by the frequency of the beat you want – 185Hz Left/195Hz Right for a 10Hz beat), or monaural/isochronic beats by generating a tone and then applying Tremeolo. You’ll notice that Generate/Tone and Effect/Tremelo provide a good select of waveforms so that many sounds/beats can be created. A Generated tone of 19.2kHz can also be used for AudioStrobe, using Tremelo in conjunction with the filtered audio or standalone.

Save the project and Export as MP3 -this will mix the four tracks (AudioStrobe Left/Right or Stereo and the audio Left/Right or Stereo tracks) into a single stereo AudioStrobe enabled music file.

Job done.

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