I've often wondered how difficult it would be for a manufacturer of a pre/ad to add the "storage" component to an existing device. I mean, there are already companies building very small embedded Linux devices. Here is one:
http://gumstix.com/platforms.html
Slap on the screen, expansion board for storage and some buttons. It's making the leap from the output of the internal AD to something like the gumstix is where I get lost.
The Rockbox folks have probably already written the code to write all the important file types, as well as, handle most all the other functions we care about. I haven't gone through it, but it's here: http://build.rockbox.org/.
inside one small case => {nice pre's > Larvy AD > gumstix running modified rockbox > flash}
Does this sound far fetched?
--Michael
Thanks for the post. Here are my initial thoughts:
The modules you point out seem to be aimed at very high speeds, at lower capacity. For audio storage, the speed for say 96KH stereo at 24 bits (which is really 6 bytes in "computer language") is near 600KB/sec. Given that one wants some margin, I would want at least 1MB/sec write speed. There is no need for 400MHz clock speed...
Also, there are all sorts of memory types. Most of the modules oriented for computer applications are volatile RAM. Volatile means the data is lost when you turn the power off, which is not good for a recorder. RAM means "random access memory", which is not needed for audio, because we "park the data" sequentially ("first come first served").
The type of memory needed is non volatile and sequential. The memory size of a standard CD (16 bits stereo at 44.1KHz) is around 650MB. So for the same CD length of time, at 24 bits you need 1/3 more, and for 96KHz 24bits you need around 2.5 times more memory... you are quickly approaching 2GB capacity...
Hard drives have huge capacity, but they tend to have limited life, and are a bit on the fragile side, though things have been improving a lot due to advancements in laptops. I like memory sticks and other flash memory technology, though they have their issues as well. With most memories, one can simply re write new data over the old data. But with flash, one needs to first erase the intended area (sort of like formatting the old floppy).
There are many other issues under consideration. It is not all that simple to design a digital device inside analog circuits.
It is always a challenge to put digital circuits near sensitive analog circuits, and with a mic pre, the challenge is the greatest. The electrical "environment" has to be extremely free of electrical interference.
As a rule, digital circuits are "noise machines", which is not an issue for all digital gear, such as computers.
But it is an issue for converters and even more so for micpre's. When your micpre is set to say 60dB gain, an input signal of 1mV (from the mic) will be amplified by 1000 (you get 1V). Clearly a 1mV digital noise getting in to the input will yield a 1V of unwanted noise... It is always a challenge to put digital circuits near sensitive analog circuits, and with a mic pre, the challenge is the greatest.
There are many more considerations and issue, but the post is getting pretty long. As you probably expected, some of the issues have known solutions, others require innovation and/or a lot of care.
Regards
Dan Lavry
www.lavryengineering.com