[sdiy] Harmonic bandwidth

[Scott Gravenhorst]

Ben Lincoln <blincoln at eventualdecline.com> wrote:
>Just to be clear, if I am making some sort of giant error, I'd 
>definitely like to know about it. Part of the reason I subscribed to 
>this list is to break the rust off of my music/audio knowledge.

I don't use Audacity, so I don't know of it's flaws, but I think that the mystery of
it's code is somewhat problematic here.  The conventional wisdom of not being able to
detect a difference when only phase is changed (but not changing) is borne of much
experimental evidence.  

IMO, if digital methods are to be used, something simple that doesn't have any
capability to adjust itself so that there is no internal mystery.  Perhaps a simple C
program that generates a .WAV file with the sinewaves for both waveforms?  This way,
others can look at the code as well as listen to the output.

>Ben Lincoln wrote:
>> I suspect that I am not using the right terminology here. I have a 
>> background in music, but I haven't worked much with audio in a number 
>> of years. When I describe altering the phase, I am not meaning that I 
>> am inverting signs (necessarily). I mean that I am adjusting the 
>> offset of one or more of the component sine waves by less than an 
>> entire cycle of that wave, so that its phase relative to that of the 
>> fundamental frequency is different.
>> For example, I created a sawtooth-like wave in Audacity using 32 sine 
>> waves (100 Hz fundamental and then the next 31 integer harmonics) - so 
>> more accurate than my Seiko DS would produce, but not as accurate as I 
>> could get out of my K5000. It's got an exponential curve instead of 
>> being a linear line because I didn't want to take the time to adjust 
>> the amplitudes of each component properly. In order to make the effect 
>> as apparent as possible, I picked a random offset (again, of less than 
>> one cycle) to adjust each of the harmonics to, rather than just using 
>> one or two like I did earlier today.
>> Here's an mp3 file of the original versus randomized phases:
>>
>> http://www.eventualdecline.com/Normal_versus_Phased_Harmonics.mp3
>>
>> Besides the obvious difference in sound, If you look at it in a 
>> spectral view, you can see that the two sections are very similar in 
>> terms of their basic content, but the second section appears 
>> "smeared". So if I am using the incorrect terminology, I think that 
>> the author of the PADsynth software is using it in the same incorrect 
>> way, because that is what I took away from his discussion of "harmonic 
>> bandwidth".
>>
>_______________________________________________
>Synth-diy mailing list
>Synth-diy at dropmix.xs4all.nl
>http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>

-- ScottG

-------------------------------------------------------------

-- Scott Gravenhorst
-- GateMan-III - FPGA Based Monophonic MIDI Synthesizer with SVF
-- PolyDaWG/8 - FPGA Based 8 Voice Polyphonic MIDI Synthesizer
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.