Hello Michael, I agree with you 100 percent about forgetting realtime and creating the wav files that can be played on my existing setup. Even in the past, when I've used MATLAB to alter signals (for example, a MATLAB-implemented phase vocoder for implant simulations), I do the processing off-line, save the file(s), and then line them up in a DAW for reproduction in a quasi-random order. What you suggest is what I've intended to do all along (although not necessarily with Linux/AmbDec until it was suggested). Maybe I've been using 'real-time' in an incorrect way. Please allow me to explain... Because some of my experiments involve adaptive test procedures, something has to 'give' during the test (during = the real-time part). The wav files, however, do NOT undergo processing once they've been lined up to play in a particular sequence via a multi-track device or DAW. An example of an adpative procedure would be trying to 'force' a speech comprehension score of 50 percent correct, and altering the SNR to achieve this score. The background noise level, signal level, or both would have to change in 'real time' (that is, change while the test is in progress) to zero in on the SNR that yields a 50 percent speech score, subject by subject. Background noise is continuous and on its own tracks, while the speech stimuli is lined up sequentially on a separate track or tracks.The background noise plays through x number of speakers at a time (let x = 6 for horizontal-only Ambisonic surround) while the speech plays through a dedicated speaker or speakers, but always one at a time. If I want the speech signal to be maintained at, for example, 75 dB SPL and the listener isn't having difficulty with the speech material at + 5 dB SNR, then the background level (all six channels) has to be elevated as the test moves forward. All I really need to do is automate the levels, not process the wav files from B-format to speaker feeds. To change the background noise level (presented through 6 speakers) means that all six channels have to change in unison and precisely by the same amount, perhaps in 2 dB steps. This is pretty straightforward with a discrete, 6-channel preamp. With a DAW, as you know, controlling six channels simultaneously requires sending them to a buss with a minimum of six channels (a 7.1 surround buss works nicely--just don't panpot anything and keep the channels totally discrete). The surround buss's master fader can adjust all channels simultaneously, and I do this in 'real-time' based listener responses. Actually, responses are recorded, and my software/hardware combo does the fader adjustment automatically.
Things get slightly more complicated when the research involves electro-acoustic simulation (EAS), which is a hybrid form of cochlear implantation. Again, I don't need to do anything with the Ambisonic processing, but 'real time' filtering comes into play. Briefly, the listener hears an acoustic signal at or below a certain f0--say 250 Hz--while the speech in the ranges of 250 Hz to 8 kHz is presented electronically via his/her implant or via a simulation. I have programmable, hardware digital filters (up to 8th order) for my filtering needs, so I don't have to do wav file processing prior to presenting the stimuli, nor do I have to run all of the multitrack channels through a VST filter. As with the aforementioned adaptive test protocol, the test subject's responses are electronically recorded, responses are fed back (after an algorithm does the decision making), and signals are adjusted accordingly to achieve a certain outcome. Ok, maybe I didn't explain this all too well, but at least it should help explain my definition of real-time, at least as far as my personal setup goes. As always, many thanks to all for the feedback, suggestions, and questions. The questions make me think harder, and perhaps my bifurcated ganglion-of-a-brain will grow at some point! Cheers! Eric C. -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20120112/991aaee6/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
