Neuros III development
From The Neuros Technology Wiki
This page is a general information-gathering resource for developers of the Neuros III, Neuros Technologies' next-generation portable audio player. This is a development page, so be bold! If you have information, links, whatever, feel free to post away. As the Neuros III moves closer to final development, content on this page will continue to change, moving from generic discussions of hardware to specific implementation details and finally to a sort of "developer's guide" for those interested in extending their Neuros.
Until we have the new, shiny Developer's Welcome page up on the wiki, this note will go here. This Wiki is designed to be a repository of information; it will be a good way to get up to speed on current trends in the development of Neuros products, and on how you can join in. However, it is not intended to be a forum of discussion. Places like the mailing lists, the forums, and IRC exist to accomodate the generation and refinement of ideas.
This page is still under development. Well, this page is always under development, but it's under more development now. Hold off on drastic edits until a decent skeletion gets set up, please.
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[edit] Feature Scope
The Neuros III is based on the DM320 Platform, so it inherits the common feature-set of that platform. Check out DM320 Platform development for more information on developing for the platform as a whole.
The Neuros must be portable, reasonably priced, and full-featured. Deciding what to include and what to drop based on these requirements is important.
[edit] Input and Output
[edit] Digital I/O
The Neuros is not being designed as a replacement for a professional digital recorder device. Therefore, features such as an ADAT Lightpipe connection is unlikely to make it in to the final design -- these connectors would be used by a tiny, tiny fraction of the total user base. If you're interested, you might check out products like these.
However, there's a ton of community interest in S/PDIF, the most common interface for digital audio IO. There are two issues under debate with S/PDIF: to include input, output, both, or neither; and whether to use coaxial or optical physical transports. At the current time, it looks like S/PDIF out is definite, and in is still under consideration. Coaxial is the more likely standard because of the reduced space requirements (it's possible to run the S/PDIF connection through a Y-splitter, much as modern digital cameras and camcorders run analog outputs through 1/8" or smaller jack plugs).
[edit] Recording Input
For the reasons listed above, in addition to the significantly increased required cost, size, and power drain of these components, a microphone preamplifier is unlikely. In addition, raising the input level in software results in nasty, nasty sound. In order to meet the needs of the majority of our customers, the Neuros will not have a microphone-level input. Instead, we may do what we did with the Neuros II: offer an external, portable mic preamp as a bundle with the Neuros III.
Whether or not we choose to offer the bundle, a high-quality line-level input is almost assured of making it into the final design. The exact specs of this line in (stereo or mono, balanced or floating, and so on) have yet to be determined.
[edit] Output Signal Path
So far, we're looking at employing a Burr Brown ADC/DAC capable of 24 bit, 96 kHz input and output, with an entirely separate phase-locked loop to generate the sample rate clock. However, past that not much else has been determined.
What follows is a portion of a discussion that occured on the Head-Fi forums on the design criteria and necessity of a line out.
"I don't believe that it is truly a software fix, and I am not sure whether it requires a different output from the headphone out. A true line out means that simply that there is as little in the signal path as possible. After the D/A conversion, the signal goes straight to the output stage -- e.g., op-amp, tube output, transformer, etc. The gain is constant on the line-out and fed to an amp.
The key here is to have as little degradation of the signal as possible, and everything that gets in the way of the signal path degrades it in some way or another. In a DAP, that means bypassing the volume control and any eq. Simply shutting those components off is not enough, as they need to be completely transparent to the signal. That's why bypassing them is so important. The purer the signal going to the amp, the better (this is all assuming that the DAP's dac and output stage are of high enough quality to make them sound good). Whether you can really bypass those components and still use the same physical output by installing an internal switch is something that I don't know about.
The importance of the line-out is for those of us who will often times use the DAP either with an external headphone amp, or to feed a home system. I'm under no illusion that the DAP's sound quality will rival that of my home cd player, which is much bigger and considerably more costly, but the line-out ensures that I am getting the best signal possible sound out of the DAP when used with external amplification."
(It should be noted that in a DSP-based system, the EQ and possibly also the volume control happen in the DSP. Bypassing the EQ is as simple as turning it off in software.)
[edit] Software
The Neuros III will almost certainly run Linux, as a member of the DM320 Platform. However, the crew of the popular Rockbox firmware replacement, which exists for a number of closed hardware players, expressed interest in running on the Neuros. Whether this collaboration will take place in full, and whether the Rockbox firmware will run on the hardware or as an alternative application within the DM320 Linux platform, is still under debate; but the two teams will certainly share code and experience whenever possible.
One of the design goals of the Neuros III is to require no software on the user's computer. This does not preclude awesome tools, such as (for example) a sync manager that works over the network, from being written; it just means that the user doesn't need special software to get the thing to work.
