After making an initial post about my research plans for psychoacoustic masking and audio steganography using the Agilent 33622A, I left for a month long trip to Europe and Iceland.  I'm back now with plenty of interesting travel experiences and a lot of bills to pay.  I am also back to full time work and we are starting undertaking major house renovations - including the addition of a purpose built electronics lab space!

I will be busy, but I'm moving forward on the psychoacoustic research.  To make measurements of acoustic audio signals I will purchase a good USB microphone.  My preference right now is the Blue Yeti microphone.  The Blue Yeti gets good reviews and is reasonably priced, plus I can use it to improve the audio quality on any future video clips I produce.

To analyse the spectrum of acoustic audio signals sensed by the microphone I'll need audio spectral analysis software.  The spectrum analyser in the MDO4104-3 only goes down to 50 kHz which is well above the top end of human hearing.  The newer MDO400B series extend the spectrum analysis down to 9 kHz, which is better, but still misses a huge swath of human hearing.  So, to analyse signals in the human hearing range, optimally 20 Hz to 20 kHz, I'm looking for a cheap or free audio spectrum analysis package.  At the moment I'm leaning toward WavePad or TrueRTA.

Does anyone have any experience with any of these products (Blue Yeti microphone, WavePad or TrueRTA), or have recommendations for other microphones and/or audio spectral analysis tools?

In my previous post I was unclear about the difference between psychoacoustic masking and audio steganography.  The difference has clarified somewhat in my mind as follows:  Psychoacoustic masking is a human auditory system phenomenon that prevents humans from perceiving audio content under specific conditions of amplitude, duration and frequency proximity to other content.  Audio steganography refers to the techniques used to purposefully embed covert data within an audio transmission by exploiting psychoacoustic masking.  As mentioned in the first blog entry on this topic, both seem to require credulity to accept as fact.  Well, there is good evidence that both work well and are exploited on a full scale commercial basis by broadcast media.  Start by reading this short article which describes the use of psychoacoustic masking by radio stations that use the BBM audience monitoring system. There are plenty of other articles and papers on both topics available on the web through your favorite search engine.


Once the microphone and audio spectrum analysis pieces arrive, I'll start making some preliminary measurements and post the results here.