Hello all,
There was a long thread....
I think we all learned at least something about IMD, air-mixing vs. electronic signal-mixing, advantages of bi- or tri-amplification etc. On the whole, a far from useless exercise. I admit to an 'incomplete' digestion of the thread's contents, but that does not detract from my above statement.
"The best lies have some truth"
I attended two hectic International acoustics conferences recently, and found much to fascinate and humble. One particularly striking research effort had been conducted by a trio of intrepid Finnish scientists who had gone to the trouble of recording, using a 'shroud' of omnidirectional microphones in an anechoic chamber, many of the instruments of the symphony orchestra (including soprano voice). Their purpose was two-fold: to investigate in high resolution the directivity characterisitcs of the various instruments, free of polluting reflections, and to prepare discrete orchestral-part recordings that could be synchronized and reproduced over a suitably complex multi-channel playback system in actual concert venues, with a view to comparing conventional 2-channel or surround-sound recordings made at these venues (made using these pre-recorded takes) from equivalent listening positions. I was treated to a demonstration (as in any conference venue, less than ideal) which proved to me the integrity of their painstaking work and the believability of the resultant 'live' playback. For anyone interested in the papers dealing with these efforts, please PM me.
I mention this because there was an unmistakable 'trend' in the results of the directivity research, suggesting that indeed, for the greater part and largely irrespective of instrument, directivity of real orchestral instruments is not so very far removed from the very familiar behaviour of standard monopole loudspeakers i.e. omnidirectional at sufficiently low frequencies, narrowing to a predictable beaming at some 'crossover point'. Interestingly, the woodwind instruments (as might be expected) exhibited the most complex and unpredictable behaviour, I expect on account of the many possible points of emanation for their sound output. This behaviour, naturally, is frequency dependent. Brass instruments display an expected almost constant directivity on the axis of the bell.
We are all now wondering: what would have been the result had various kinds of organ pipe been tested?. I will harrass the excellent scientists of my recent acquaintance towards this end; meanwhile the question remains: how do pipes of various pitch and nature project their sound (fixed frequency and amplitude, of course) into the hall or casework? We might aid in the ultimate realism of reproduction by an awareness of these physical properties.
The other point is the one raised by Martin: the various approaches to high-resolution sampling do capture in a very substantial way the 'character' of the pipe. This surely can apply to close-sampling as well as relatively distant. Of course pipes are not meant to be 'listened to' at point-blank range and, if recorded in this manner, had best be allowed to 'develop' in either a real or virtual acoustic. I'll add my two cents worth on the issue of signal mixing effects on dry samples — it (signal-mixing distortion) is obvious and objectionable using even very high-quality 2-channel systems. IMD as such is of course a quantifiable problem; if one is limited to a two channel source (or prefers to be limited to such) then we rely on the competence of the relevant reproduction equipment. The case of the chromatically sampled pipe organ is special, and we need not be so absolutely bound.
Conventional 2-channel playback (or, for that matter, it's extensions ito 5.1, 7.1 etc.) must be acknowledged to have its own problems. I have more than once on this forum mentioned the ravages of inter-aural crosstalk and state-of-the-art means to ameliorate this problem. On the other hand, the establishment of of a believable ambient/reverberant field is something that can (or should) command the attention of all enthusiasts, not just 'domestic' players or listeners. In some senses the home user has a certain advantage in this regard, at least potentially, against the predicament of the large-venue installation which even so may lack a really generous reverberant field.
What is best? Principles developed for hi-fidelity listening can be gainfully employed. One thing we must acknowledge is that, even when equipped with two additional 'surround' channels, we should not (ideally) attempt to push this audio data out into the room through a pair of widely-spaced loudspeakers. Our hearing mechanism cannot make much of this in terms of a believable soundfield — though the data is unquestionably of value and can be better deployed. How? Especially considering the relatively fixed seating position of the primary listener (in this case the player...) what we can establish, with the appropriate hardware/software is a rear 'stereo dipole' — that is, two loudspeakers positioned very close together and fed with crosstalk-cancelled signals. The rear soundfield will occupy a broad hemisphere with the directionality of the various later reflections intact (something that cannot be achieved through conventional reproduction). Those who might object that large venues exhibit statistically diffuse soundfields should do some critical listening in these spaces.
By definition, these sorts of recordings are 'wet'. The same sort of subjective result can be had through the use of appropriate convolution engines and a multi-channel output and side-rear loudpeaker array. Of course, the convolution data, even if from the exact same organ-installation venue, is uncorrupted by the inevitable presence of 'frontal sound' in the rear-hemisphere 'channels' present in conventional surround-sound recordings. If opting for 2-channel frontal reproduction, the closely-spaced speaker + crosstalk cancellation approach will deliver huge dividends as well.
What of dry sample reproduction in domestic, relatively damped acoustical conditions? Here we can easily differentiate between the frontal and rear soundfields, with one important included observation. The 'dry' pipe sound, naturally would be expected to emanate from the front (except for those occasional remote-rank situations such as I encountered recently in Melbourne), though even this is necessarily complemented with a significant contribution of case and frontal room ambience/reverb. This must be provided, if not in the recording, then by subsequent processing (appropriate impulse responses will do nicely). The 'greater' soundfield can be similarly and authentically presented, preferably with a bank af angularly displaced loudspeakers fed with discrete convolved signals. In a properly damped room, the results can be very believable and powerful. In this there is a 'crossover' between the requirements of the wet- and dry sample user. The fact that rear reverberation is unavoidably captured in either 2-channel or 4-channel (front L-R) 'wet' sample libraries, while regrettable, is not terminally destructive to the beauty or usefulness of these virtual instruments, anymore than would be the case for a conventional stereo recording of the same instrument and venue. We might, however, consider the advantages in addressing the binaural behaviour of our hearing mechanism when recordings (CD-type or sample) are made. Many issues with signal-to-noise ratio and directional issues can be eliminated effectively through recording techniques that focus on the frontal sound and suppress the rear, preferably through acoustic baffling (as directional microphones have many anomalous behaviours in addition to their 'hesitant' bass response) with later addition of convolved ambience/reverberation. A body of empirical evidence should encourage us in this direction. A believable ambience is indeed the linchpin of our efforts and hopes in this regard. Having this successfully established, much else can be less than optimal to little negative effect.
I am conscious of the length of this contribution, and promise not to make a habit of it..... (I await HW 4 as eagerly as the next man),
Cheers to all,
Stephen.
There was a long thread....
I think we all learned at least something about IMD, air-mixing vs. electronic signal-mixing, advantages of bi- or tri-amplification etc. On the whole, a far from useless exercise. I admit to an 'incomplete' digestion of the thread's contents, but that does not detract from my above statement.
"The best lies have some truth"
I attended two hectic International acoustics conferences recently, and found much to fascinate and humble. One particularly striking research effort had been conducted by a trio of intrepid Finnish scientists who had gone to the trouble of recording, using a 'shroud' of omnidirectional microphones in an anechoic chamber, many of the instruments of the symphony orchestra (including soprano voice). Their purpose was two-fold: to investigate in high resolution the directivity characterisitcs of the various instruments, free of polluting reflections, and to prepare discrete orchestral-part recordings that could be synchronized and reproduced over a suitably complex multi-channel playback system in actual concert venues, with a view to comparing conventional 2-channel or surround-sound recordings made at these venues (made using these pre-recorded takes) from equivalent listening positions. I was treated to a demonstration (as in any conference venue, less than ideal) which proved to me the integrity of their painstaking work and the believability of the resultant 'live' playback. For anyone interested in the papers dealing with these efforts, please PM me.
I mention this because there was an unmistakable 'trend' in the results of the directivity research, suggesting that indeed, for the greater part and largely irrespective of instrument, directivity of real orchestral instruments is not so very far removed from the very familiar behaviour of standard monopole loudspeakers i.e. omnidirectional at sufficiently low frequencies, narrowing to a predictable beaming at some 'crossover point'. Interestingly, the woodwind instruments (as might be expected) exhibited the most complex and unpredictable behaviour, I expect on account of the many possible points of emanation for their sound output. This behaviour, naturally, is frequency dependent. Brass instruments display an expected almost constant directivity on the axis of the bell.
We are all now wondering: what would have been the result had various kinds of organ pipe been tested?. I will harrass the excellent scientists of my recent acquaintance towards this end; meanwhile the question remains: how do pipes of various pitch and nature project their sound (fixed frequency and amplitude, of course) into the hall or casework? We might aid in the ultimate realism of reproduction by an awareness of these physical properties.
The other point is the one raised by Martin: the various approaches to high-resolution sampling do capture in a very substantial way the 'character' of the pipe. This surely can apply to close-sampling as well as relatively distant. Of course pipes are not meant to be 'listened to' at point-blank range and, if recorded in this manner, had best be allowed to 'develop' in either a real or virtual acoustic. I'll add my two cents worth on the issue of signal mixing effects on dry samples — it (signal-mixing distortion) is obvious and objectionable using even very high-quality 2-channel systems. IMD as such is of course a quantifiable problem; if one is limited to a two channel source (or prefers to be limited to such) then we rely on the competence of the relevant reproduction equipment. The case of the chromatically sampled pipe organ is special, and we need not be so absolutely bound.
Conventional 2-channel playback (or, for that matter, it's extensions ito 5.1, 7.1 etc.) must be acknowledged to have its own problems. I have more than once on this forum mentioned the ravages of inter-aural crosstalk and state-of-the-art means to ameliorate this problem. On the other hand, the establishment of of a believable ambient/reverberant field is something that can (or should) command the attention of all enthusiasts, not just 'domestic' players or listeners. In some senses the home user has a certain advantage in this regard, at least potentially, against the predicament of the large-venue installation which even so may lack a really generous reverberant field.
What is best? Principles developed for hi-fidelity listening can be gainfully employed. One thing we must acknowledge is that, even when equipped with two additional 'surround' channels, we should not (ideally) attempt to push this audio data out into the room through a pair of widely-spaced loudspeakers. Our hearing mechanism cannot make much of this in terms of a believable soundfield — though the data is unquestionably of value and can be better deployed. How? Especially considering the relatively fixed seating position of the primary listener (in this case the player...) what we can establish, with the appropriate hardware/software is a rear 'stereo dipole' — that is, two loudspeakers positioned very close together and fed with crosstalk-cancelled signals. The rear soundfield will occupy a broad hemisphere with the directionality of the various later reflections intact (something that cannot be achieved through conventional reproduction). Those who might object that large venues exhibit statistically diffuse soundfields should do some critical listening in these spaces.
By definition, these sorts of recordings are 'wet'. The same sort of subjective result can be had through the use of appropriate convolution engines and a multi-channel output and side-rear loudpeaker array. Of course, the convolution data, even if from the exact same organ-installation venue, is uncorrupted by the inevitable presence of 'frontal sound' in the rear-hemisphere 'channels' present in conventional surround-sound recordings. If opting for 2-channel frontal reproduction, the closely-spaced speaker + crosstalk cancellation approach will deliver huge dividends as well.
What of dry sample reproduction in domestic, relatively damped acoustical conditions? Here we can easily differentiate between the frontal and rear soundfields, with one important included observation. The 'dry' pipe sound, naturally would be expected to emanate from the front (except for those occasional remote-rank situations such as I encountered recently in Melbourne), though even this is necessarily complemented with a significant contribution of case and frontal room ambience/reverb. This must be provided, if not in the recording, then by subsequent processing (appropriate impulse responses will do nicely). The 'greater' soundfield can be similarly and authentically presented, preferably with a bank af angularly displaced loudspeakers fed with discrete convolved signals. In a properly damped room, the results can be very believable and powerful. In this there is a 'crossover' between the requirements of the wet- and dry sample user. The fact that rear reverberation is unavoidably captured in either 2-channel or 4-channel (front L-R) 'wet' sample libraries, while regrettable, is not terminally destructive to the beauty or usefulness of these virtual instruments, anymore than would be the case for a conventional stereo recording of the same instrument and venue. We might, however, consider the advantages in addressing the binaural behaviour of our hearing mechanism when recordings (CD-type or sample) are made. Many issues with signal-to-noise ratio and directional issues can be eliminated effectively through recording techniques that focus on the frontal sound and suppress the rear, preferably through acoustic baffling (as directional microphones have many anomalous behaviours in addition to their 'hesitant' bass response) with later addition of convolved ambience/reverberation. A body of empirical evidence should encourage us in this direction. A believable ambience is indeed the linchpin of our efforts and hopes in this regard. Having this successfully established, much else can be less than optimal to little negative effect.
I am conscious of the length of this contribution, and promise not to make a habit of it..... (I await HW 4 as eagerly as the next man),
Cheers to all,
Stephen.
Last edited by Stephen Phillips on Sat Oct 09, 2010 11:16 pm, edited 1 time in total.
Yours,
Stephen Phillips
______________________
More at: http://www.inspiredacoustics.com
Latest instruments: Scots | Kolozsvar | Esztergom | PAB
Stephen Phillips
______________________
More at: http://www.inspiredacoustics.com
Latest instruments: Scots | Kolozsvar | Esztergom | PAB