I want to make an audio looper with up to 10 seconds of loop. I don't need to do any processing, just bring in from ADC, store, send to DAC at the appropriate time.

Am I missing any options for the RAM I need, as explained next?

I plan on using a microcontroller, mostly because I'm looking for MCU projects to do to work on my programming skills, and because I don't really need to do anything to the audio samples except play them back. Assuming 16 bit samples and 40kS/s, this works out to 6250Kb of RAM for a maximum 10 second loop. I like the idea of using SRAM with SPI communication, but the largest I find is 1Mb. I'd rather not have to use 6 or 7 individual RAM chips. On the other hand, DRAM comes in much larger sizes for a single chip, but they all seem to use parallel communication and have much higher pin count and smaller pitch, all of which makes it more of a pain to use in a DIY project.

Are there any other options out there for ~6Mb of RAM over SPI?

 

Straight digitization wave capture, ADC to memory, memory to DAC, is a brute-force method that is very demanding on memory space.
Check out WinBond sound recorder chips such as ISD4004-16MPY which will record 16 minutes of voice.
What kind of sound quality do you need?

 

I might use a SD card in SPI high speed mode using raw blocks for a circular buffer if I needed brute-force audio storage for a simple looper/delay. Memory size is not a problem and the W/R speeds can easily handle HD audio signals.

https://github.com/sergev/LiteBSD/wiki/SD-Card-Benchmark

 

Another approach would be a teensy+audio board+sd card
teensy 3.2
audio board

And then use their audio library

 

I want to make an audio looper with up to 10 seconds of loop. I don't need to do any processing, just bring in from ADC, store, send to DAC at the appropriate time.

Am I missing any options for the RAM I need, as explained next?

I plan on using a microcontroller, mostly because I'm looking for MCU projects to do to work on my programming skills, and because I don't really need to do anything to the audio samples except play them back. Assuming 16 bit samples and 40kS/s, this works out to 6250Kb of RAM for a maximum 10 second loop. I like the idea of using SRAM with SPI communication, but the largest I find is 1Mb. I'd rather not have to use 6 or 7 individual RAM chips. On the other hand, DRAM comes in much larger sizes for a single chip, but they all seem to use parallel communication and have much higher pin count and smaller pitch, all of which makes it more of a pain to use in a DIY project.

Are there any other options out there for ~6Mb of RAM over SPI?

Is using FLASH an option? If so, how about: https://www.digikey.com/product-det...cs/W25Q80JVSNIQ-TR/W25Q80JVSNIQ-CT-ND/6236444

 

I was just looking at flash memory (which SD cards seem to be an implementation of) but it doesn't look like the typical write speeds are fast enough. For instance, one I just looked at had about 350us write time for a single byte. At a sample rate of 40kHz, the samples come every 25us.

As for the quality, I'm shooting for 16 bit, at least 40kHz, so that sound recorder IC wouldn't work.

 

Why does the write speed matter? Aren't you just reading when playing back?

 

I was just looking at flash memory (which SD cards seem to be an implementation of) but it doesn't look like the typical write speeds are fast enough. For instance, one I just looked at had about 350us write time for a single byte. At a sample rate of 40kHz, the samples come every 25us.

As for the quality, I'm shooting for 16 bit, at least 40kHz, so that sound recorder IC wouldn't work.

NOR flash does have slow write speeds while raw NAND flash W/R operations are a lot more complicated.
http://aturing.umcs.maine.edu/~meadow/courses/cos335/Toshiba NAND_vs_NOR_Flash_Memory_Technology_Overviewt.pdf

A typical SDCARD (with its internal DISKONACHIP memory controller) made with NAND flash takes the most of the dirty management details out of the programming equation. You should be writing and reading full 512 block buffers to/from loop memory with hopefully a controller with DMA for the ADC, DAC and SPI devices.

 

Why does the write speed matter? Aren't you just reading when playing back?

No. This is a performance device which has an instrument input. I would hit a footswitch to start recording what I'm playing, hit it again to stop recording and immediately play/loop it. There are several made for guitarists, like this one:

http://www.tcelectronic.com/ditto-looper/

I'm not sure how that pedal manages 5 minutes of loop time for a $100 pedal. It must have pretty low fidelity. I play keyboard, so I need a wider bandwidth, and I'm shooting for approximately CD-quality audio.

 

You can get Psuedo static RAM in 64 and 128Mbit packages. Interface is 8 bits wide and looks fairly simple. The ISSI IS66... is less than $7 for a 128Mbit. Not sure how much glue logic but I bet a micro with DMA could interface to it. The bad news - BGA only.