Author Topic: Analog or digital?  (Read 1582 times)

xorophone

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Analog or digital?
« on: August 25, 2016, 04:06:05 PM »
Hello! I'm building the Leviathan delay from Etcher's Paradise and right now I'm designing a waterslide decal for it. This delay is fully analog right? I want to write "Analog Delay" on it, but of course it has to be analog for that. I'm 99% sure it is, but I just want to make sure the PT2399 isn't digital or something.

Also, if anyone wants to give me an explanation on how to easily identify this in the future, I'd be really happy.

Thanks!

somnif

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Re: Analog or digital?
« Reply #1 on: August 25, 2016, 04:27:39 PM »
The 2399 is a digital chip which emulates analog style delay. Sorry to disappoint.

somnif

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Re: Analog or digital?
« Reply #2 on: August 25, 2016, 04:39:58 PM »
Now that Im not trying to type on a phone, I can talk a bit more about it. The PT2399 is a digital device. It stores an incoming signal in memory and processes it in an attempt to replicate the decay pattern of an older analog delay. Here is the diagram of the chip:



That big black box of voodoo in the middle is where all the signal processing happens.

Compare this to analog delays. The oldest style of analog delay is, well, tape. Store a sound on a tape and run it back across another head to play the sound again. Works great, but its bulky, expensive, and fragile.

To work around this, engineers thought to use banks of capacitors to store and eject the signal instead. A lot of capacitors. The earliest forms of this used a rotating belt to hold capacitance and discharge it as necessary. This was complicated by the fact that Air would render the trick useless, so the whole mess had to be submerged in oil. See: http://www.geofex.com/Article_Folders/oil_can_delays.htm

To get more convenient, we started to make banks of capacitors microscale and constructed integrated circuits of them. These we called "Bucket Brigade Devices", and this class makes up the bulk of what we call "Analog delays".  Basically the signal gets stored in a cap, and moved one step down the line with each tick of a clock cycle. Depending on the chip, it may have 256, 512, or 1024 steps (usually), which contributes to the max time of delay. However, this storage ability is imperfect, so you get some high end bleed off each repeat, so the echos get "darker" as they go. Most people consider this pleasing to the ear, and its this darkening that the PT2399 means to replicate (with varying degrees of success). http://www.electrosmash.com/mn3007-bucket-brigade-devices



So, how to tell at a glance? If it has a BBD chip (MN300X, most frequently, though older SAD1024 chips do popup in schematics) its "analog". If its PT2399, or some other purpose built chip, assume its digital.

Fun fact, the Belton "Brick" reverb unit is essentially 3 PT2399s playing off one another. Its digital too!
« Last Edit: August 25, 2016, 04:43:05 PM by somnif »

xorophone

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Re: Analog or digital?
« Reply #3 on: August 26, 2016, 01:34:27 PM »
Now that Im not trying to type on a phone, I can talk a bit more about it. The PT2399 is a digital device. It stores an incoming signal in memory and processes it in an attempt to replicate the decay pattern of an older analog delay. Here is the diagram of the chip:



That big black box of voodoo in the middle is where all the signal processing happens.

Compare this to analog delays. The oldest style of analog delay is, well, tape. Store a sound on a tape and run it back across another head to play the sound again. Works great, but its bulky, expensive, and fragile.

To work around this, engineers thought to use banks of capacitors to store and eject the signal instead. A lot of capacitors. The earliest forms of this used a rotating belt to hold capacitance and discharge it as necessary. This was complicated by the fact that Air would render the trick useless, so the whole mess had to be submerged in oil. See: http://www.geofex.com/Article_Folders/oil_can_delays.htm

To get more convenient, we started to make banks of capacitors microscale and constructed integrated circuits of them. These we called "Bucket Brigade Devices", and this class makes up the bulk of what we call "Analog delays".  Basically the signal gets stored in a cap, and moved one step down the line with each tick of a clock cycle. Depending on the chip, it may have 256, 512, or 1024 steps (usually), which contributes to the max time of delay. However, this storage ability is imperfect, so you get some high end bleed off each repeat, so the echos get "darker" as they go. Most people consider this pleasing to the ear, and its this darkening that the PT2399 means to replicate (with varying degrees of success). http://www.electrosmash.com/mn3007-bucket-brigade-devices



So, how to tell at a glance? If it has a BBD chip (MN300X, most frequently, though older SAD1024 chips do popup in schematics) its "analog". If its PT2399, or some other purpose built chip, assume its digital.

Fun fact, the Belton "Brick" reverb unit is essentially 3 PT2399s playing off one another. Its digital too!

Good thing I decided to ask here before I made the decals! Thank you for the explanation, somnif! I might write "PT2399 Delay" (under "Leviathan") or something similar then, because digital doesn't sound as cool as analog. ;)

HamSandwich

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Re: Analog or digital?
« Reply #4 on: August 26, 2016, 10:38:41 PM »
There was a rash of 'analog delays' when builders first started using the PT2399 in the mid 2000's (iirc) that got everyone all excited. A lot of them used this karaoke chip. It did not end well for a lot of builders when the truth came out.

Jebus

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Re: Analog or digital?
« Reply #5 on: August 27, 2016, 01:56:26 AM »
There was a rash of 'analog delays' when builders first started using the PT2399 in the mid 2000's (iirc) that got everyone all excited. A lot of them used this karaoke chip. It did not end well for a lot of builders when the truth came out.

Yeah, some companies also got into that (mostly the cheap plastic pedals). Joyo, Behringer and so on.

HamSandwich

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Re: Analog or digital?
« Reply #6 on: August 27, 2016, 10:45:44 AM »
There were unfortunately some bigger names too. I remember back in Harmony Central's heyday, there was a big to-do about it. I remember one that was pink, $200+ dollars and was labeled 'analog'. Tsk tsk