hey guys i am looking for a good digital reverb design. i am completely clueless about it, i guess it has to pass the following stages: adc -> some "storage" option -> some chip that reads the memory a certain number of times -> dac
i hint this might be a little harder than your average diy project, maybe, but i am looking foward to trying good designs. if you could give me a hint i would truly appreciate it.
thanx
Luciano
i hint this might be a little harder than your average diy project, maybe, but i am looking foward to trying good designs. if you could give me a hint i would truly appreciate it.
thanx
Luciano
I was looking for the same kind of product about a month ago.
Some years back there were analog bucket brigade chips for this use but they have apparently gone out of production.
An alternative limited only to delay effects should be A/D followed by FIFO memory and D/A, all of this coordinated by a local clock and some glue logic.
I choose to follow the DSP route which provides also much more processing possibilites like filtering, tremolo, equalization, flanger etc.
It implies higher costs and a substantial learning curve but I felt worth it. This project will be adressed towards year's end / next year.
Rodolfo
Some years back there were analog bucket brigade chips for this use but they have apparently gone out of production.
An alternative limited only to delay effects should be A/D followed by FIFO memory and D/A, all of this coordinated by a local clock and some glue logic.
I choose to follow the DSP route which provides also much more processing possibilites like filtering, tremolo, equalization, flanger etc.
It implies higher costs and a substantial learning curve but I felt worth it. This project will be adressed towards year's end / next year.
Rodolfo
There are Reverberation Amplifiers on ebay all the time that go cheap and they often use those analog bucket brigade shift registers. I have a nice one scored at a yard sale (Sansui or maybe Pioneer) It has a way out time tunnel display on the front panel. I also have a Radio Shaft mixing console with this form of echo built in and a separate Radio Shaft echo box also using bucket brigade. These could maybe be coaxed from my paws with offers of cash.
ingrast said:
can you tell me more about the dsp?? i have found one, the tas3103 but it seems a bit complex... can you tell me how you use it?? or which one do you use??
and how you solder it, since it has those little legs??
thanx in advance
DSP for reverb
Luciano:
Getting into DSP is not the casual type of project. DSP works by processing digitized signals on the fly with algorithms in turn derived from a mathematical formalization of signal theory.
If you have a maths and physics background, I can point you reference material to check in this respect, and to application specific literature and producs.
To start actual work, you should select a manufacturer and product family that better suits your needs, and purchase a developement kit which usually bundles a card with the DSP chip and support circuitry, a cable for communicating the card and your computer, and software both for download / debug and for program developement. Prototype kits usually cost several hundred dollars depending on brand and model.
Rodolfo
Luciano:
Getting into DSP is not the casual type of project. DSP works by processing digitized signals on the fly with algorithms in turn derived from a mathematical formalization of signal theory.
If you have a maths and physics background, I can point you reference material to check in this respect, and to application specific literature and producs.
To start actual work, you should select a manufacturer and product family that better suits your needs, and purchase a developement kit which usually bundles a card with the DSP chip and support circuitry, a cable for communicating the card and your computer, and software both for download / debug and for program developement. Prototype kits usually cost several hundred dollars depending on brand and model.
Rodolfo
digital reverb
Luciano:
Stirred by your enquiry, I checked some parts and found a rather decent slapback/reverb, even basic chorus can be readily built from a few tens of dollars worth of components.
I requested samples and will be back in a few days with a more definite idea.
Rodolfo
Luciano:
Stirred by your enquiry, I checked some parts and found a rather decent slapback/reverb, even basic chorus can be readily built from a few tens of dollars worth of components.
I requested samples and will be back in a few days with a more definite idea.
Rodolfo
Basically this can be achieved without a DSP chip, using cheap standard components.
You implement a ring buffer which consists of an address counter and a static RAM. Then add a parallel ADC and DAC, with associated analog signal conditioning. The databus of ADC, DAC and RAM would be connected. A clock and decimal counter provides the timing for the steps of operation:
1. Read a sample from the ring buffer and transfer it to the DAC
2. Read a sample from the ADC and transfer it to the RAM
3. Advance the address counter
4. back to step 1
Feedback (for multiple echos) and mixing the original with the delayed signal would be done in the analog domain.
The delay time can be adjusted by resetting the address counter at adjustable positions or by changing sampling frequency (tricky).
A long time ago I built such a beast based on 8bit Ferranti DACs and ADCs. Must have been one of my first projects. It was based on an article in an electronics magazine which went out of business in the 80s.
You implement a ring buffer which consists of an address counter and a static RAM. Then add a parallel ADC and DAC, with associated analog signal conditioning. The databus of ADC, DAC and RAM would be connected. A clock and decimal counter provides the timing for the steps of operation:
1. Read a sample from the ring buffer and transfer it to the DAC
2. Read a sample from the ADC and transfer it to the RAM
3. Advance the address counter
4. back to step 1
Feedback (for multiple echos) and mixing the original with the delayed signal would be done in the analog domain.
The delay time can be adjusted by resetting the address counter at adjustable positions or by changing sampling frequency (tricky).
A long time ago I built such a beast based on 8bit Ferranti DACs and ADCs. Must have been one of my first projects. It was based on an article in an electronics magazine which went out of business in the 80s.
Digital reverb harware project
OliverD:
You are quite right with the proposed configuration. I should suggest a FIFO type memory for the delay element, for they are made with that purpose in mind to simplify circuitry. You don’t need for example address generator and latching of input / output data since FIFOs are dual ported.
What I have in mind nonetheless is something a little more involved, short of a more accurate realization that mostly makes sense with a DSP chip instead of specially built hardware.
A more realistic reverberation consists of an initial delayed echo, followed by several decaying closely spaced secondaries. More sophisticated implementations involve pre-delays and various mixings of secondaries at different time intervals.
A basic yet workable hardware realization can be accomplished for example with a first delay stage – tunable from 10 to 40 ms corresponding to what is known as “slap back”, and a second stage tunable from 3 to 10 ms with feedback to accomplish the decaying secondaries train.
I have ordered a set of samples including 74V225 1Kx18 FIFO (U$ 8.- ea.) for the second stage, 74V245 4Kx18 FIFO for the first stage (U$ 8.50 ea.), PCM1802 96 KHz / 24 bit A/D converter (U$ 3.35 ea.) and DSD1791 192 KHz / 24 bit D/A converter (U$ 3.15 ea.). Add to this some TL074 low noise opamps for antialiasing filters, post-conversion filters and you are mostly done.
An inexpensive and interesting addition should be to enable not only variable clocking speed (to vary delay) but also to modulate it with a low frequency to achieve a basic chorus effect and similars. The design should end up with lots of switches and knobs, but musicians use to love to have lots of things to tweak with. (interestingly, it is fairly easier to provide lots of switches and knobs in a purely hardware approach than a software based one !)
I will pursue this development in the next weeks (as soon as I receive the samples and design and build a prototype PCB).
If there is interest in this subject, I will post more details (tentative schematics etc.) and will of course welcome any suggestions you deem worth considering.
PT2399
I did some search on this part and found neither Digi-Key nor Newark carry it. It is probably the type of discontinued or not widely available part I should not try in a new design. A reference to it mentions it is rather noisy too.
Rodolfo
OliverD:
You are quite right with the proposed configuration. I should suggest a FIFO type memory for the delay element, for they are made with that purpose in mind to simplify circuitry. You don’t need for example address generator and latching of input / output data since FIFOs are dual ported.
What I have in mind nonetheless is something a little more involved, short of a more accurate realization that mostly makes sense with a DSP chip instead of specially built hardware.
A more realistic reverberation consists of an initial delayed echo, followed by several decaying closely spaced secondaries. More sophisticated implementations involve pre-delays and various mixings of secondaries at different time intervals.
A basic yet workable hardware realization can be accomplished for example with a first delay stage – tunable from 10 to 40 ms corresponding to what is known as “slap back”, and a second stage tunable from 3 to 10 ms with feedback to accomplish the decaying secondaries train.
I have ordered a set of samples including 74V225 1Kx18 FIFO (U$ 8.- ea.) for the second stage, 74V245 4Kx18 FIFO for the first stage (U$ 8.50 ea.), PCM1802 96 KHz / 24 bit A/D converter (U$ 3.35 ea.) and DSD1791 192 KHz / 24 bit D/A converter (U$ 3.15 ea.). Add to this some TL074 low noise opamps for antialiasing filters, post-conversion filters and you are mostly done.
An inexpensive and interesting addition should be to enable not only variable clocking speed (to vary delay) but also to modulate it with a low frequency to achieve a basic chorus effect and similars. The design should end up with lots of switches and knobs, but musicians use to love to have lots of things to tweak with. (interestingly, it is fairly easier to provide lots of switches and knobs in a purely hardware approach than a software based one !)
I will pursue this development in the next weeks (as soon as I receive the samples and design and build a prototype PCB).
If there is interest in this subject, I will post more details (tentative schematics etc.) and will of course welcome any suggestions you deem worth considering.
PT2399
I did some search on this part and found neither Digi-Key nor Newark carry it. It is probably the type of discontinued or not widely available part I should not try in a new design. A reference to it mentions it is rather noisy too.
Rodolfo
Yes I assume it (pt2399) is obsolete or obscure
I mention it because it just seems so simple.
( I have no exerience with it )
It and it's obscure BBD chips seem to be available here
http://www.smallbearelec.com/Ordering/ICsDelay.htm
I eagerly await a more substantial design- as yours appears to be
😉
Dave
I mention it because it just seems so simple.
( I have no exerience with it )
It and it's obscure BBD chips seem to be available here
http://www.smallbearelec.com/Ordering/ICsDelay.htm
I eagerly await a more substantial design- as yours appears to be
😉
Dave
EPE magazine had a project called the "polywotsit", which used a PIC with ADC built in and an external DAC. Several effects are switch-selectable, all implemented in firmware. It uses 8bit converters, not state-of-the-art but probably equivalent to a bucket brigade chip. You might get some ideas from it, link is here
edit;- BTW it's December 2001 edition.
edit;- BTW it's December 2001 edition.
I will make an initial design in the weekend and post a condensed schematic.
It should be fine to have more input from others in the forum regarding desirable / undesirable features before proceeding to prototyping.
Suggestions welcome.
Rodolfo
It should be fine to have more input from others in the forum regarding desirable / undesirable features before proceeding to prototyping.
Suggestions welcome.
Rodolfo
Well, I know nothing of DSPs, so I don't really know what's possible with them. Maybe it's possible to make this an all-in effects-box?
To solve your lots-of-buttons problem, instead of hooking up one button to one I/O pin, make a resistor chain out of them and use the DSPs ADC to check which button was pressed (asuming a DSP has got an ACD of course).
Here's the idea. You could change the voltage drop to .2 or .1 volt per button to allow up to 49 switches on one I/O pin.
To solve your lots-of-buttons problem, instead of hooking up one button to one I/O pin, make a resistor chain out of them and use the DSPs ADC to check which button was pressed (asuming a DSP has got an ACD of course).
Here's the idea. You could change the voltage drop to .2 or .1 volt per button to allow up to 49 switches on one I/O pin.
An externally hosted image should be here but it was not working when we last tested it.
Digital reverb preliminary draft
Here is a preliminary draft design for a hardware based digital reverb processor.
The basic structure is a dual delay chain based on 24 bit A/D converters (18 bits effectively used), 4096 and 1024 x 18 bit FIFO memories, and 24 bit D/A converters (18 bits effectively used).
Delay length is continuously selectable from a variable 3:1 ratio sampling clock generator, and a switch selectable 1:4 FIFO clock (may be jumper selectable for 1:2 ratio). The sampling / shift clock may be further modulated in depth and rate by a low frequency oscillator to generate chorus effects.
The first stage delays the incoming signal from 10 to 32 ms or 64 to 128 ms adjustable as indicated. This signal may be mixed at a selectable level with the "dry" input to generate a "slap-back" effect.
The signal delayed by the first stage is further delayed by a second one (5 to 15 ms) in a feedback loop. Delay varies concurrently with the first stage, since the stereo A/D and D/A converters of which one channel is devoted to each delay stage, have a common sampling clock. This stage in effect adds multiple copies of the incoming signal at multiples of the loop delay and with decaying amplitude. Loop gain is adjustable so as to shorten - lengthen the decay rate. This signal is in turn mixed in an adjustable level with the "dry" and "slap-back" signals to generate the output.
As it usually turns out, the design ended a bit more involved than foreseen, so it will take some extra days to arrive to a workable schematic. The selected low cost A/D and D/A converters generate / expect multiplexed serial digital audio streams that must be deserialized / serialized for writing and reading the FIFO buffers. These chips also are basically conceived for programmability by an external controller, though they default to usable configurations upon reset. So it is necessary to juggle a little with these configurations and clocking - data routing to arrive to a workable design.
Will keep posting details as work progress, and of course will hear any suggestions that may arise.
Rodolfo
Here is a preliminary draft design for a hardware based digital reverb processor.
The basic structure is a dual delay chain based on 24 bit A/D converters (18 bits effectively used), 4096 and 1024 x 18 bit FIFO memories, and 24 bit D/A converters (18 bits effectively used).
Delay length is continuously selectable from a variable 3:1 ratio sampling clock generator, and a switch selectable 1:4 FIFO clock (may be jumper selectable for 1:2 ratio). The sampling / shift clock may be further modulated in depth and rate by a low frequency oscillator to generate chorus effects.
The first stage delays the incoming signal from 10 to 32 ms or 64 to 128 ms adjustable as indicated. This signal may be mixed at a selectable level with the "dry" input to generate a "slap-back" effect.
The signal delayed by the first stage is further delayed by a second one (5 to 15 ms) in a feedback loop. Delay varies concurrently with the first stage, since the stereo A/D and D/A converters of which one channel is devoted to each delay stage, have a common sampling clock. This stage in effect adds multiple copies of the incoming signal at multiples of the loop delay and with decaying amplitude. Loop gain is adjustable so as to shorten - lengthen the decay rate. This signal is in turn mixed in an adjustable level with the "dry" and "slap-back" signals to generate the output.
As it usually turns out, the design ended a bit more involved than foreseen, so it will take some extra days to arrive to a workable schematic. The selected low cost A/D and D/A converters generate / expect multiplexed serial digital audio streams that must be deserialized / serialized for writing and reading the FIFO buffers. These chips also are basically conceived for programmability by an external controller, though they default to usable configurations upon reset. So it is necessary to juggle a little with these configurations and clocking - data routing to arrive to a workable design.
Will keep posting details as work progress, and of course will hear any suggestions that may arise.
Rodolfo
Attachments
Devil_H@ck said:
Yes, the idea is a full DSP implementation allows for essentially unlimited effects, being the processor speed the only constraint. This includes stereo panning, ping-pong, chorus, reverb, tremolo, flanger etc. etc.
With respect to the multiple switch interfacing solution, it is a clever and compact one with the only limitation it works for only a switch at a time. The one closer to the A/D port effectively blinds out the others. When I mentioned it was easier to interface switches and knobs to hardware based projects, I meant they do their work directly on the circuit, whereas a software approach requires scanning / decoding and processing, all of wich is a chore and takes processor resources.
Rodolfo
johnnyx said:
I could not locate the project in the link, but nonetheless you are right in the appreciation. 8 bits are probably rather coarse in S/N for an instrument level effects processor.
Rodolfo
davesaudio said:
I was aware of the site, as you may have noticed the chips are NOS (New Old Stock) meaning they are discontinued.
All I could find on the polywhatsit
http://homepages.nildram.co.uk/~starbug/files/polywhatsit.zip
source code only?
anybody got a schematic?
http://homepages.nildram.co.uk/~starbug/files/polywhatsit.zip
source code only?
anybody got a schematic?
Re;- polywotsit
I think you have to buy a reprint.. but no matter, I have the article and can scan it. The software (maybe should be firmware) can be downloaded free from the site, as you have seen. The PCBs (1 analogue & 1 digital) are available for only £7.61 for the pair according to the magazine with the article.
If anyone is interested, send me an e-mail from the link on my user info. There is no way to include attachments there, but it will generate a normal e-mail that will accept attachments in a reply. It's fairly large, 8 sides of A4, and includes PCB patterns. I'll see if I can send it uncompressed.
I have two TDA1097, made by Mullard, 1536 stage BBD chips that I never got round to using. They are pre-production prototypes. I have the datasheet too, and I have two TDA1022. I experimented with the latter but found them noisy, almost certainly due to the spaghetti layout I used. My layouts are better now. If you want to experiment with them, send your address in the e-mail. I have no time for it now.🙁 🙂
I think you have to buy a reprint.. but no matter, I have the article and can scan it. The software (maybe should be firmware) can be downloaded free from the site, as you have seen. The PCBs (1 analogue & 1 digital) are available for only £7.61 for the pair according to the magazine with the article.
If anyone is interested, send me an e-mail from the link on my user info. There is no way to include attachments there, but it will generate a normal e-mail that will accept attachments in a reply. It's fairly large, 8 sides of A4, and includes PCB patterns. I'll see if I can send it uncompressed.
I have two TDA1097, made by Mullard, 1536 stage BBD chips that I never got round to using. They are pre-production prototypes. I have the datasheet too, and I have two TDA1022. I experimented with the latter but found them noisy, almost certainly due to the spaghetti layout I used. My layouts are better now. If you want to experiment with them, send your address in the e-mail. I have no time for it now.🙁 🙂
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