Hardware ideas
From Earfilter
An Earfilter is intended to be a hardware device of some kind with a stereo audio input (probably line level) and a stereo audio output (probably headphone level). For compactness and ease of use, these connections should probably be made via 3.5mm stereo jack sockets. In between the input and the output, analogue to digital conversion, signal processing, and digital to analogue conversion must take place, in that order.
In order to be portable, usable anywhere, Earfilter is intended to be powered by battery or via a mains adaptor. Depending upon the battery technology used, it may incorporate a battery-charging circuit.
Below, some of the possible electronic hardware platforms for this are outlined.
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[edit] Microcontroller-based options
Some hardware platforms that might be suitable.
[edit] Microcontrollers with integrated A/D and D/A
These may offer the most compact, power-efficient solution, but they are not cheap.
- Sharc DSP chips, made by Analog Devices. (Here's an example of what Sharcs can do.)
- Blackfin DSP chips, also made by Analog Devices. (Here is some info about using Blackfins in portable devices.)
- DSP56367 DSP chips - aka Symphony DSP chips - made by Freescale (formerly Motorola). (Here is a review of an audio processor based on this chip.)
- Gumstix, especially with the Audiostix 2 expansion board. So far, this is probably the lowest-cost option, but at $140-$210 (as of early November 2008), still not a cheap one.
- Beagle Board, similar in cost to the Gumstix above. $149 as of Jan 2009, with integrated stereo audio input/output.
[edit] Standalone A/D or D/A converters and suitable microcontrollers
It may be cheaper to cobble something together out of separate integrated circuits. If so, one needed task would be to decide which A/D or D/A architecture(s) to use.[1]
[edit] Other options
If the Earfilter software is implemented in a way that would work on a variety of architectures, then it would be possible to turn consumer devices into Earfilters, for instance:
- Laptops (especially small ones, e.g. XO or EEE). Disadvantages: weight; size; lack of line-level audio inputs in some cases; proprietary audio drivers in some cases. Advantages: increasing ubiquity; eliminates or reduces need for earfilter.org hardware development.
- Mobile phones / PDAs. Disadvantages: insufficient processor power in some cases; lack of line-level audio inputs in most cases; proprietary hardware. Advantages: ubiquity; portability.
- Ready-made portable FX units (e.g. the Korg Pandora, the manual for which is available here). Disadvantages: proprietary hardware & software, so hard to modify; in-built FX algorithms may not be suitable for Earfilter; may not have stereo line-level inputs that connect to the FX chain. Advantages: portability; processor power; professional packaging.
