Propeller for Guitar Effects?
Mark Buckingham
Posts: 4
I'm a guitarist, computer programmer, and part-time burner of fingers via a soldering iron.
I'm basically hoping to design & build a guitar multi-effects processor, and I'm wondering if the propeller has enough horsepower to pull it off...
I think I need the following:
16 or 24 bit A/D and D/A conversion
ability to process at least 3 effects at a time from the following:
--> echo
--> chorus (combines original signal with one that is slightly in & out of tune)
--> flanger (more or less same thing as chorus, but with different timing)
--> pitch shifting (take the input note and move it up or down by +/- 12 notes)
--> reverb
front panel controls to control the effects
ability to save combinations of effects & settings as patches
(maybe) midi control
stereo output is a plus, but not a deal breaker.
I don't need anything like distortion or amp modelling. That's part of why I want to do this myself... Most of the units on the market try to do too much.
the effects have to have very little latency... When I play a note, it has to come out without a noticeable delay.
Does this sound like something that the propeller can pull off?
Thanks!
I'm basically hoping to design & build a guitar multi-effects processor, and I'm wondering if the propeller has enough horsepower to pull it off...
I think I need the following:
16 or 24 bit A/D and D/A conversion
ability to process at least 3 effects at a time from the following:
--> echo
--> chorus (combines original signal with one that is slightly in & out of tune)
--> flanger (more or less same thing as chorus, but with different timing)
--> pitch shifting (take the input note and move it up or down by +/- 12 notes)
--> reverb
front panel controls to control the effects
ability to save combinations of effects & settings as patches
(maybe) midi control
stereo output is a plus, but not a deal breaker.
I don't need anything like distortion or amp modelling. That's part of why I want to do this myself... Most of the units on the market try to do too much.
the effects have to have very little latency... When I play a note, it has to come out without a noticeable delay.
Does this sound like something that the propeller can pull off?
Thanks!
Comments
I think it should be able to do what you are listing. How do you intend to pull it off? have you seen what the propeller can do as far as sound? I got mine to sing and speak using the available codes.
I saw the examples you're talking about... That made me think I have a chance of this working.
I think the hard part is really going to be coding the effects themselves, but assuming I can find examples of the effects elsewhere, then it's just programming. (ha)
So... To expand my what I was saying earlier, I'm thinking of using the cogs like this:
#1 - gets data from A/D converter and puts into a input buffer
#2 - processes chorus or flanging
#3 - processes delay
#4 - processes reverb
#5 - processes some other effect
#6 - monitors midi stream to switch patches
#7 - monitors knobs, footswitches, etc and updates parameters as needed
#8 - gets data from output buffer and sends to D/A converter
Just a thought,
However, I have been very impressed by the audio samples that people in this forum have contributed, so I think the prop could be an excellent single-chip solution.
I've never heard of a CVSD before... I'll have to look into that.
Thanks!
·
The design has the following features:
-········· Propeller core
-········· 1MByte SRAM standard (room for 1.5MByte on the PCB)
-········· 44kHz 24-bit sampling (2 input channels, 2 output channels)
-········· 4 control knobs
-········· 16x2 LCD screen
-········· 2 stomp switches
-········· 2 stomp indicator LEDs
-········· 1 1/4 inch audio input
-········· 1 1/4 inch audio output
-········· 1 multipurpose 1/4 inch audio jack (can be used as either a second output (for stereo effects) or as an additional input (for modulation effects etc.))
-········· NTSC Video out
-········· Micro USB
-········· 9V DC Power in
-········· Headphone out (mini phono)
-········· RJ45 expansion port (for potentially adding things like external foot pedals)
-········· Aluminum chassis
·
The pedal is designed for production, so I’ll be making it available as a completed unit.· All the source will of course be available so that people can create their own effects and hack away to their heart’s content.· I’m also developing a windows application which lets you do a lot of high level control (effect configuration etc) from the PC side.
·
I have a demo song but I sampled it at a very high bitrate (since it was an audio quality demo) so its too large to post here (6MB).· I’ll have to see if I can resample to a lower bitrate and post it.
Post Edited (epmoyer) : 11/22/2007 5:13:28 AM GMT
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Help to build the Propeller wiki - propeller.wikispaces.com
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Would you mind publishing the schematics? Not that I want to copy it, but I'm just interested how you did it and what you used.
Nick
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Never use force, just go for a bigger hammer!
The DIY Digital-Readout for mills, lathes etc.:
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Give us some Rock 'n' Roll!
That looks perfect!
I think I might just wait until your pedal is ready. I could spend my time building a good tube preamp to put in front of it instead.
Any idea when you'll have units ready for sale?
cheers
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<FONT>Steve
What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!
You didn't feel too hamstrung by the lack of hardware multiplies?
I needed a lot of RAM to support long delays and complex reverb effects.· If you want to implement multiple delays at the same time (like a reverb and a digital delay), then both effects allocate chunks of the same SRAM pool, so that puts pressure on the size.· The main reason for going with 1MB was that I wanted to be able to support a K.T.Tunstall style loop effect (ala Black Horse and the Cherry Tree).·
While the samples are 24 bits I found that I used 32 bit words in SRAM to store samples because the indexing math was more straighforward (although if one is pressed for space one can always decide to take on the complexity of the indexing and buy themselves another 25% of space).· On the other hand, I do all the effect math in 32 bits, so a reverb or delay which appears after another effect will want to use 32 bit words anyway to avoid rounding down the precision of previous steps (even though the final mixdown goes back to 24 bits, in general it's preferable to maintin your highest bit width until the end of the chain).
Yes, the LCD is a carryover from my Hydra debugger widget, but in this implementation it has a full 8 bit interface since I wasn't·limited to the·available signals on the Hydra expansion port.
Well, I wasn't·intending to announce so soon.· I only spilled the beans because Mark raised the subject.· If I do release schematics to the general public I'll do it when the device is released.· If I don't release schematics to the general public I'll still include the schematics with the pedal.·
Hmmm.· I should think by late January.· The hardware is done, and the chassis design is done (but I don't have one in my hands yet to test).· The remaining work is on manuals, finishing the OS, polishing the sample effects, and finishing the Windows app.·
I do apologize for the threadjack. Sorry Mark!
Well, you're certainly correct that the primary limitation in using the Prop for a signal processor is it's lack of a multiply instruction.·· When I started this project I would alternately flip back and forth between loving the idea and saying to myself "what the heck am I doing choosing a processor with no multiply?!?!?".· Well, as we all know by now the Propeller consistenly out-performs its apparent class, and this case is no different.· Sure, you take a time hit to do a multiply, but you gain so very much from the Prop's unique architecture that on balance it makes for a really cool effects platform.· I had the idea to do an open-source effects pedal some years ago, but it wasn't until the Prop came along that I realized I could finally do it in a way that had very expansive possibilities and free development tools.· Who in their right mind would have ever designed an effects pedal with video out?· Once you decide to use a Prop, how could you not?· And once you have a guitar pedal with video out, just imagine all the weird things you can do with it.
Today I use the multiply for the·tremolo effect, and for output volume scaling.··In both cases the time hit was insignificant relative to the load on the associated Cog.
Post Edited (epmoyer) : 11/23/2007 5:23:24 AM GMT
Distortion normally uses some filtering to affect which frequency ranges get distorted.· This one doesn’t yet, so it’s a little rough.· I also didn't have these effects written to use the knobs for parameter alteration at the time, so I had to dial in the delay time by iteratively changing my constants and recompiling;· It’s not quite matched to the song tempo, but pretty close.· Chorus usually uses some sample interpolation to avoid the noise of sliding the delay line tap point back and forth at discrete sample steps.· The current version doesn't,·but the noise is not very noticeable in this recording.· If I play harder it becomes more evident.
Love the demo, very cool.
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Thanks for the info. One other thing: are you using the prop counters for a/d and d/a?
Btw, forgot to mention earlier, but awesomely cool project!
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Cheers,
Simon
www.norfolkhelicopterclub.co.uk
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)
BTW: I type as I'm thinking, so please don't take any offense at my writing style
well done.
Baggers.
Keep up the excellent work!!
The SRAM is accessed in parallel, 8 bits at a time.· There is a PLD on the board which manges the SRAM, LCD, and some other misc glue functions.· You load the SRAM address into the PLD, and then it will autoincrement the address as you read/write bytes.· For sequential bursts you pay the address setup hit once and then just pull or push data a byte at a time.
I have a dedicated device on the board to do a/d and d/a.· The device serializes the sample data, so I use the prop counters to gerate the serial data clocks and to retrieve/export the relevant sample data.· I figured that with a dedicated device I would both get cleaner audio and keep more cogs free for effects processing.
A tuner is in the cards.· Pitch detection will be done in software.
Hope you stop by the forum again soon and give us an update.
I think people are starting to miss you around here.
Also is that you playing in the demo song?
If so, then I'd have to say your a pretty darn good musician. [noparse];)[/noparse]
If you plan on selling some of these, then I'll buy one from ya and gig with it!
--Andrew Arsenault.
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Share the knowledge: propeller.wikispaces.com
Lets make some music: www.andrewarsenault.com/hss
Yes, I'm going to make them available; everything has been designed for manufacturability. The chassis is build like a tank so the pedal is very gig-worthy. I set out from the beginning to make something that could be used live and get banged around a fair bit. This thing is a labor of love for me so I made the pedal I would want if someone else were building it instead. That drove the requirements for durability, a back-lit screen, lots of knobs, high quality stomp switches, and a nice windows GUI app.
yerpa58 asked me a little while ago if I'd put together a mailing list for notices about pricing, availability, etc. on the guitar pedal. It's now a list of one [noparse];)[/noparse] If anyone else would like to be on the mailing list just drop me a PM and I'll include you as well. I'm going to make some "pre-release" units available before all the software is finished. All the hardware has been debugged and tested so the hardware platform is done, but there are a lot of software pieces and documentation to finish before the whole package is commercially ready. The pre-release units will ship with the current O/S and effects set so that gear-heads like me (and probably you, if you're reading this) can get up and hacking away before some of the more polished software tools are complete. Early adopters also have a chance to get their effects onto the first "proper release" production CD, and they'll get all the final versions of the software when it releases. The final software collection will give a fair bit of functionality to non-programmers, enabling them to tap into the shared community of published effects and to configure them without learning spin or assembly. I'll poll for a head count before I do the pre-production run. More to follow.
I was reading through some of my old posts and I noticed that I never discussed the distortion algorithm used for the demo song.
Things like Chorus, Tremolo, and Delay effects are pretty straightforward; they lend themselves to relatively easy digital implementations. Guitar distortion effects are very analog beasts. They got their start by pushing analog amplifiers into their overdrive region where the amps became non-linear and the output wave shape became "distorted" relative to the input. When distortion caught on people started designing amps and pedals to generate it, all of which fundamentally involved operating some analog component(s) (tubes, transistors, diodes) in a region of operation where the device(s) "broke down" and became non-linear in some interesting way. The behavior of those analog components varies with frequency, and can vary with the drive level, or with their short term "history" of activity, and can distort the positive going wave differently than the negative going wave. All of that analog stuff can be very tricky to model digitally, which is why purists detest digital distortion pedals and opt for analog devices.
The distortion I wrote for the demo is almost the simplest possible algorithm for distortion; all it does it apply a sinusoidal roll-off to a linear transfer function. Its simple, symmetrical, non-frequency dependent, and sounds... terrible! Better distortion is in the works.
Post Edited (epmoyer) : 1/14/2008 8:54:04 AM GMT
Anyway. A very simple form of Digital distortion that I always liked was the low-bitrate distortion.
It's when you take a digital signal at some higher sampling rate and over-sample it at a much lower rate.
Say 44.1K into only 8k with no antianalising.
It produces complex forms of modulation and differential ringing that can add a really neat LoFi sound to many instruments. Seems to be popular with some forms of modern light electronic music.
The only way to get close to that sound in the analog world is by taking a carrier and amplitude modulating it with your signal and running the output through a tight bandpass filter tuned to your carrier to remove some of the sideband's energy. Something you might be able to do with something like an analog vocoder from the 70s. [noparse];)[/noparse]
Thanks epmoyer!
--Andrew Arsenault.
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Share the knowledge: propeller.wikispaces.com
Lets make some music: www.andrewarsenault.com/hss
I'm a little behind where I expected to be on releasing the fist production build; chalk that up to my pesky "real job" getting in the way [noparse];)[/noparse] .
Nevertheless, I'm very excited about the way things have turned out.· One of the big challenges on this project was to make the Howler accessible to 3 classes of users:
··· 1) Uber-users who want to create (i.e. code) custom applications more-or-less "from scratch".
··· 2) Super-users who want to create (i.e. code) custom "effects".
··· 3) Regular users who want to make use of the community of published work without having to write code.
I wanted class 3 to be able to mix/match/load/remove/configure effects without even launching the Propeller IDE, but it seemed like a pipe dream.· A couple weeks ago I figured out how to to make it happen, and an extremely flexible development & delpoyment environment has been the result.
What I finally realized was that effects would always be written in ASM since spin cannot keep up with the 44kHz sample rate (it is possible however to write hybrid apps where graphing, etc. is performed in spin; and a large portion of the Howler OS is written in spin).· Because the effects themselves are ASM code, its possible to play a trick...· I·created a functional unit of code called the Howler "MODULE", which is basically an ASM image that occupies a single cog.· A MODULE may be "unitary" and contain a single (generally complex) EFFECT, or it may be "compound" and contain several (generally simpler) EFFECTs.· Because a MODULE is ASM code, it is possible for the O/S to relocate it (in RAM), store it in EEPROM, copy it over the serial port, and whenever appropriate load it into a cog and start it.· Working in conjunction with a companion windows app called the "Howler Workbench", the Howler O/S is now able to manage a "pool" of available MODULEs some of which may be compiled into the O/S (called "STATIC MODULEs"; there can be up to 4) and a heaping pile of which may be stored in upper EEPROM (called "DYNAMIC MODULEs").
A class 2 developer creates a MODULE by compiling it into the O/S build as a STATIC MODULE and thinkering around until it works.· Inside Howler Workbench the module appears as a block which can be wired to other system resources by drawing lines to connect their CONDUITs (the inputs and outputs of functional blocks).· Once the STATIC MODULE is debugged and working, the Howler Workbench application can be used to upload it to the PC's disk; at which point it becomes a DYNAMIC MODULE.· DYNAMIC MODULES can then be downloaded to the Howler hardware where they are stored in EEPROM as a large available "pool" from which to draw.
Class 3 users will be able to get new DYNAMIC MODULEs from the web, load/shuffle/archive/manage them with the Workbench, and use the Workbench to string together combinations of different effects (from different DYNAMIC (or STATIC) MODULEs) to create PATCHes.· A PATCH is a specific configuration of Effects (from MODULES) with a specific CONDUIT interconnection scheme (akin to "wiring").
There are a couple of configuration structures which support the MODULES;· I won't go into detail here, but they will be very well documented in the manual.· One is a "MODULE DESCRIPTOR" which describes the MODULE to the OS (its required resources, its·name, its CONDUITs,·their types, etc.), and the other is a "MODULE INTERFACE·BLOCK" which is a data structure in RAM thorough which the MODULE's·information flows (mostly·the CONDUIT data, plus a couple other command/control elements).
Below is·a screen shot of the current Workbench build.
Post Edited (epmoyer) : 2/5/2008 7:00:47 AM GMT
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Cheers,
Simon
www.norfolkhelicopterclub.co.uk
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)
BTW: I type as I'm thinking, so please don't take any offense at my writing style
It's Looking really fantastic! Can't wait to try one. [noparse]:)[/noparse] I really like the idea of being able to program the unit with a modular approach. That way you can program it with only the effects you use, For my pedal steel guitar I use a PODXT as an effects unit. It's a great unit but it has so many options (I only use a few) it's often hard to select exactly what you want. For a pedal steel player such as myself it's almost impossible to use a pot (when you have picks on your hand, both your hands and feet are engaged all at once) when your playing. It's a challange when playing live and often I would turn the knob to get a new effect but would end up past the position I wanted and my part in the song would be over before I got it sorted out. [noparse]:)[/noparse] A few years ago I built a PIC based MIDI control unit (with 8 bushbuttons) to send messages to the PODXT and can use it while it's cliped it onto the leg of my pedal steel guitar. The advantage is that I can press buttons as I play to select specific chanels on the PODXT that were pre-programed for the effects I wanted. I believe I will have the same type of problem controlling your unit but will wait until I see the schematic to see what my options are. Their's always a way around it.
Please keep us updated when you have time.
Bob
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References:
Pedal Steel Guitar: en.wikipedia.org/wiki/Pedal_steel_guitar
PODXT: line6.com/podxt/
I play a PODXT Live myself! I just love line6; those guys do an awesome job.
I've been working on a website for the pedal. I expect to go live with it this week; just tweaking some of the content right now. There will be some new screenshots of the windows app there and some more info about the pedal.
As for foot control, the "standard" method of changing patches on the Howler is to click both buttons simultaneously with your foot to enter "patch select" mode, and then the buttons become up/down patch selects. The beauty of open source is of couse that you can do whatever the heck you want, so If you have a situation where you're playing on stage and you need to be able to switch between patches simply with your feet rather than using the buttons to control aspects of the effects themselves, then you can just patch the OS to keep you in patch select mode all the time.
There's also an expansion port on the unit whch could be used to interface to an analog pedal or a box with a bunch of button on it. The interface is basically digital serial, so one would have to roll their own interface board but it's not too complicated. I'll play around with that interface once the pedal is in production and see where I can take it, but the documentation is all there for anyone to use it.
Thanks for the encouragement! It's been a long road and I'm exremely excited to be nearing completion.
Yes the week is over and you must be ready
I did find another guitar effects unit called the Howler: The Howler Effects Pedal from Maven Peal - It provides Tone, Gain, Peal and Volume controls it usues a 18 volt adapter,
www.mrbluesguy.com/the-howler-effects-pedal-from-maven-peal/
Still can't wait
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Aka: CosmicBob