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What storage medium do "off the shelf" guitar looping pedals use?
Kalcifer:
I'm looking into making my own guitar looping pedal; however, I'm slightly stumped (but mostly just curious) on what storage medium to use to store the audio that's being recorded.
Random DIY projects that I have seen online use an SD card to store the audio, but for some reason I have the feeling that a professional product like a looping pedal wouldn't use an SD card as a storage medium. I should note, however, that I am not against using an SD card, I'm just curious what is actually done in the industry. I would guess that they use a FLASH IC or something of the like, but I haven't found anything with any substantial capacity as of yet.
My other concern is with the endurance of the SD card, but I wouldn't imagine that you could run into the problem of the storage medium failing since it would take ages to perform millions of write cycles when it's just a looping pedal.
james_s:
I don't know what the pedals use, but I've worked on samplers that use SRAM or DRAM for storage. If I were trying to design a looping pedal I'd look at SRAM since it's easy to work with and you probably don't need a huge capacity.
Kalcifer:
--- Quote from: james_s on July 24, 2020, 04:27:54 am ---I don't know what the pedals use, but I've worked on samplers that use SRAM or DRAM for storage. If I were trying to design a looping pedal I'd look at SRAM since it's easy to work with and you probably don't need a huge capacity.
--- End quote ---
With a 10bit ADC, and a sampling rate of 44.1kHz, you' be looking at 441kbps of data flowing to the storage device. For only 1 minute of audio that's ~26.5Mb of data. With those kinds of numbers I'd say that 1GB of storage would be a safe amount. Now with SRAM, I don't think numbers like 1GB even exist. There's gotta be a way to reduce the size of the recording though because 26.5Mb seems ridiculous to me.
james_s:
1GB? For a guitar pedal? How long of a loop are you wanting to have? How many bits do you really need? I'd have thought a second or two at most. If you want to save a bunch of samples then SD would make sense but the actual active sample would almost have to be in RAM of some sort.
Obviously compression is an option, mp3 and other compression codecs have been around for a long time and there are hardware solutions to implement them with less powerful micros.
Kalcifer:
--- Quote from: james_s on July 24, 2020, 05:48:18 am ---1GB? For a guitar pedal? How long of a loop are you wanting to have? How many bits do you really need? I'd have thought a second or two at most. If you want to save a bunch of samples then SD would make sense but the actual active sample would almost have to be in RAM of some sort.
Obviously compression is an option, mp3 and other compression codecs have been around for a long time and there are hardware solutions to implement them with less powerful micros.
--- End quote ---
Well if you have say 6 loops each only 10 seconds long, that's a minute of uncompressed data. At the very least I would want 100Mb I'd say, and again that gets pricey or very difficult to find.
A loop could be a second, or it could be 10 seconds or 30 seconds or more. It just depends on what you're doing. 1 or two seconds for a loop wouldn't be very useful.
And you could transfer it in blocks. Record a chunk of audio into RAM, and then write it all to the storage device while you're recording the next chunk.
As for compression, can you use it on the fly? I feel like it would use up for too much resources to be used while recording and playing in real time.
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