3 ms·

Would it be continuous time if not clocked, e.g. switches or 555 timer feeding into logic gates, and levels just switch when they switch. Of course no logic tr

by dspig 7y ago

Would it be continuous time if not clocked, e.g. switches or 555 timer feeding into logic gates, and levels just switch when they switch. Of course no logic transitions are actually instant...

squeaky-clean 7y ago
The clock is what defines the sampling rate of the delay, so a 555 is just a simpler version of what they already use. The true audio is always moving continuously. When the BBD receives a clock signal, it samples the incoming audio, and to reconstruct that audio as accurately as possible you have to play it back at that same rate it was sampled in. Very similar to how digital (PCM) audio works, except using charged capacitors instead of bits in a digital memory. If you don't clock it at all, you'll just be sending out the constant voltage equal to whatever your first capacitor has charged, which results in no audible sound. You can adjust your clock speed and have it play back at speeds slower or faster than the incoming rate, with the pitch changing too, just like slowing a record or tape machine. The output isn't really discrete though, only the internals, and even then like you say, even logic transitions aren't actually instant (but at a rate so much faster than audio we ignore it). The BBDs use filters on both the input and output that remove the very high-end of the audio range (a lowpass filter). These filters will be made to match or be lower than the current clock rate [0]. One before going into the BBD removes any frequencies too high to be stored accurately (an anti-aliasing filter), and then one after the BBD removes any high frequencies which were created by the near-instant shapes of the capacitors discharging (a reconstruction filter). These means your output audio is "continuous", but also has zero frequency content above your filter cutoff (okay there's a teeny amount of information, nothing in reality is perfect). To create the delay effect you take a long line of them (usually 512-4096) and the length of your delay is equal to the number of "buckets" times your clock rate. If you had a near infinite amount of buckets and ran them so fast there was no loss in fidelity from the sampling rate, you'd basically have a tape delay. The fun thing about BBDs though is that they don't always pass on their charge to the next bucket perfectly. So longer delay lines mean introducing more errors accumulating as your audio passes through the delay line. A near-infinite BBD would turn into audio mush. Though you can still get a very high number of buckets and a very high clock rate for near digital fidelity, but at that point it's getting more expensive than just using a digital effect, and you're ditching the unique charm of a nice effect. Here are some more detailed explanations of a bbd [1] [2] The posts by Richard Crowley in [2] are particularly cool to the HN audience I'd hope. > Curiously enough, BBD were a pre-cursor to EEPROM, DRAM, and FLASH RAM. Microscopic capacitors are used to store the data. In the case of DRAM, the capacitors aren't terribly good, and they must be "reminded" (refreshed) on a regular basis (many times per second). Very similar to BBD. [0] okay technically 1/2 the clock rate because of nyquist-shannon, I just mean it will be linked to the sampling rate. [2] https://www.electrosmash.com/mn3007-bucket-brigade-devices https://www.electrosmash.com/mn3007-bucket-brigade-devices [3] https://www.gearslutz.com/board/geekslutz-forum/897599-how-does-bbd-store-audio.html https://www.gearslutz.com/board/geekslutz-forum/897599-how-d...

by dspig 7y ago

Would it be continuous time if not clocked, e.g. switches or 555 timer feeding into logic gates, and levels just switch when they switch. Of course no logic transitions are actually instant...

squeaky-clean 7y ago

The clock is what defines the sampling rate of the delay, so a 555 is just a simpler version of what they already use. The true audio is always moving continuously. When the BBD receives a clock signal, it samples the incoming audio, and to reconstruct that audio as accurately as possible you have to play it back at that same rate it was sampled in. Very similar to how digital (PCM) audio works, except using charged capacitors instead of bits in a digital memory. If you don't clock it at all, you'll just be sending out the constant voltage equal to whatever your first capacitor has charged, which results in no audible sound. You can adjust your clock speed and have it play back at speeds slower or faster than the incoming rate, with the pitch changing too, just like slowing a record or tape machine. The output isn't really discrete though, only the internals, and even then like you say, even logic transitions aren't actually instant (but at a rate so much faster than audio we ignore it). The BBDs use filters on both the input and output that remove the very high-end of the audio range (a lowpass filter). These filters will be made to match or be lower than the current clock rate [0]. One before going into the BBD removes any frequencies too high to be stored accurately (an anti-aliasing filter), and then one after the BBD removes any high frequencies which were created by the near-instant shapes of the capacitors discharging (a reconstruction filter). These means your output audio is "continuous", but also has zero frequency content above your filter cutoff (okay there's a teeny amount of information, nothing in reality is perfect). To create the delay effect you take a long line of them (usually 512-4096) and the length of your delay is equal to the number of "buckets" times your clock rate. If you had a near infinite amount of buckets and ran them so fast there was no loss in fidelity from the sampling rate, you'd basically have a tape delay. The fun thing about BBDs though is that they don't always pass on their charge to the next bucket perfectly. So longer delay lines mean introducing more errors accumulating as your audio passes through the delay line. A near-infinite BBD would turn into audio mush. Though you can still get a very high number of buckets and a very high clock rate for near digital fidelity, but at that point it's getting more expensive than just using a digital effect, and you're ditching the unique charm of a nice effect. Here are some more detailed explanations of a bbd [1] [2] The posts by Richard Crowley in [2] are particularly cool to the HN audience I'd hope. > Curiously enough, BBD were a pre-cursor to EEPROM, DRAM, and FLASH RAM. Microscopic capacitors are used to store the data. In the case of DRAM, the capacitors aren't terribly good, and they must be "reminded" (refreshed) on a regular basis (many times per second). Very similar to BBD. [0] okay technically 1/2 the clock rate because of nyquist-shannon, I just mean it will be linked to the sampling rate. [2] https://www.electrosmash.com/mn3007-bucket-brigade-devices https://www.electrosmash.com/mn3007-bucket-brigade-devices [3] https://www.gearslutz.com/board/geekslutz-forum/897599-how-does-bbd-store-audio.html https://www.gearslutz.com/board/geekslutz-forum/897599-how-d...