Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Sat Jan 23, 2010 9:27 am Post subject:
Digital Noise Synth Idea
The block diagram depicts the basic idea I have for a digital noise synth.
The top signal chain generates white noise which is filtered by an SVF with fixed configurable Q and allows Fc to be modulated by the middle signal chain and a bias value.
The bottom signal chain generates modulation values to control an NCA in the top signal chain.
An envelope generator contours the amplitude of the top chain.
This is an experiment and may change as I develop it.
The first version will be a single voice, but if it works and is fun and useful, I will probably expand it to a polysynth of 4 or 8 voices.
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Sun Jan 24, 2010 12:54 pm Post subject:
This is an update with more detail in the drawing.
The amplitude window is a shifter mechanism that I use to accomodate widely differing amplitudes because of the increased gain at Fc with higher Q values. Without the window shifter, the signal can overflow binary wrap which sounds horrible. The detector and indicator tells me whether a "patch" is doing bad things at which point I can adjust with the amplitude window and then compensate with the level control.
Noise_Synth.gif
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Updated Design Block Diagram
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Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Sun Feb 07, 2010 4:44 pm Post subject:
Well, I finally got some sound out of the testbed for this synth. So far, I have the top row of logic running and I just got sound. The noise generator is generating noise, the filter is filtering, and the ADSR is ADSRing.
The structure is evolving into something a bit different than the block diagram, still very similar though. I'll post a new one when I finalize it. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
I'm curious about the sound of this thing
Are you seeing it as being used mostly with high Q (or self oscillation even) for the filters in order to produce controllable pitched sounds?
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Sun Feb 07, 2010 7:10 pm Post subject:
DrJustice wrote:
I'm curious about the sound of this thing
Are you seeing it as being used mostly with high Q (or self oscillation even) for the filters in order to produce controllable pitched sounds?
DJ
--
Yes and no, this synth was not intended for pitched sounds,but they should be possible. I envision it as a synth to be used for noise type sounds like wind and hopefully thunder and perhaps other odd noise based sound. These sounds would probably be generated using low Q, even as low as 1.0.
The Q of this filter can go as high as 150, so if it's set high enough some hopefully interesting pitched noise sounds might be produced.
The synth does not use the MIDI note number to set any of the filters' Fc, so it won't be able to play keyboard melodies as designed. Pitched sounds being driven by the Fc modulation source are possible - Perhaps flying insect noises ?
I may add code to use the MIDI note number information to feed the bias input. That would allow this synth to play keyboard melodies... _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Sat Feb 13, 2010 6:49 pm Post subject:
What I have working is one chain of noise -> SVF -> NCA. NCA is modulated by an ADSR. The sample below uses the filter in lowpass mode with moderately low Q. This will sound pretty basic, noise into a resonant filter...
The noise source is a 64 bit maximal length LFSR.
I hope to get some modulation stuff done this weekend.
But at least I can get this much filtered noise out of it.
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Mon Feb 15, 2010 1:29 pm Post subject:
I just got Fc modulation by filtered noise working.
It seems that high frequency noise modulation of high frequency noise - still sounds mostly like noise. More interesting is when lower frequency noise is used to modulate Fc of high frequency noise. I use "high frequency" to indicate audio range.
So I will extend the range of the frequency slider. Currently I have 4 ranges, each lower setting is another octave lower Fc. I believe that 8 range settings will be quite useful, with extension to more lower frequencies.
Nice low low frequency noise modulating Fc with moderate Q (about 5) gives a nice howling wind sound.
When I get this part of the synth nailed down, hopefully later today, I will post a sample of some howling wind and perhaps other sounds I find while testing. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Tue Feb 16, 2010 4:29 pm Post subject:
Here's a screen shot of the patch editor for the NoiseSynth. It shows a fictitious patch.
I wrote this in VB.NET Express Edition (which is free from Microsoft). The program communicates with the synth hardware over a USB connection to the board. The messages are formatted exactly like system exclusive messages and could be transmit over MIDI. This is more convenient because I don't need to figure out how to interface with a MIDI connection that also supports performance data.
NoiseSynthPatchEditor.jpg
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NoiseSynth Patch Editor screen shot.
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Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 270
Posted: Wed Feb 17, 2010 1:19 am Post subject:
I'm not following this in detail, but the wind I heard in the chatroom sounded very convincing. I mentioned that one could control the voices with Boolean Sequencers and got a positive response from Scott, so we'll see what happens.
Les _________________ "Let's make noise for peace." - Kijjaz
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Wed Feb 17, 2010 8:03 am Post subject:
Yes, Les, a sequencer could be added to the logic in place of the MIDI trigger logic for a self contained noise unit. Push a button - out comes sound that is sequenced over time for variety.
I'm thinking of a companion synth that does FM bells as wind chimes where the chimes have random timbre, random pitch and random strikes.
The current version of NoiseSynth is MIDI driven which facilitates testing in my lab/studio. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Wed Feb 17, 2010 12:30 pm Post subject:
audiodef wrote:
Do you have this in a VST somewhere? I'd love to use it.
Ah, sorry, I'm not a VST guy. Once it's finalized, I'll post the Verilog, so a courageous person versed in VST and Verilog might translate it? _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Wed Feb 17, 2010 1:11 pm Post subject:
It's a MIDI synth, so it responds to MIDI keypress note events.
Currently, the lowest 8 keys (on my wavestation) are mapped to the 8 instruments. Each instrument can be separately programmed, but all 8 have the same structure.
Another future version will eventually allow tonal melodies to be played by using higher Q values on the audio path SVF. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 237
Posted: Wed Feb 17, 2010 2:24 pm Post subject:
Ah, heh. An FPGA is hardware. It is a system of mostly identical logic blocks, several thousand of them, who's function is defined by the bit file loaded into the device. It "assumes the identity" of the logic defined in the Verilog (or VHDL) source code. It's behavior while in operation is exactly like an ASIC (Application Specific Integrated Circuit) or any other IC that is developed for a specific purpose.
Verilog, the hardware definition language I use, looks a lot like C so it might be easy to assume that the end result is software, but it is not. It allows allocation of the FPGA resources to execute the writer's end purpose.
I think of an FPGA as a pile of "logic Lego". It has RAMs, multipliers, adders, multilplexors, and basic logic functions as well as logic function generators (that you define) that can be connected together in the same way someone might connect logic devices like CD4XXX parts.
This is not to be confused with a CPU which executes one instruction after another in a linear sequence. An FPGA _can_ do that - but a lot of it's charm comes from the fact that parallel logic is possible. For example, in a CPU, if you want to AND two data elements together and then AND two other elements together, you're usually stuck with two instruction cycle times. Something like that is easily done in an FPGA, both operations simultaneously. Arithmetically, this is attractive because an FPGA will have several hardware multipliers inside of it, each of which can execute in parallel with the others.
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima Last edited by JovianPyx on Wed Feb 17, 2010 5:13 pm; edited 2 times in total
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