Personally I'm happy to call 24/96 good enough for me. My ears wouldn't benefit from 384kHz and I'd reserve the "Low-end" label for 16/44.1
Its certainly good enough for the vast majority of people. And there's plenty of evidence to suggest that there's no benefit going any better, other than marketing spin of course
The iPod is a great way of having a lot of music on the move.
Oh absolutely agree – these little portable media players are perfect for that.
But I use my home system which wasn't particularly cheap so I'd appreciate the benefit that 24-bit support in iTunes brings – I.e. improved dynamic range (when the producers wake up).
The issue of dynamic range in modern recordings is a hot topic in pro audio circles at the moment. If anyone's interested there is a talk this coming Thursday in Cambridge on precisely this subject:
I think normal conversations can tolerate a surprisingly low quality connection – look at the phone system. So I wouldn't say Skype or other VoIP systems suffer too badly.
I find a multi-meter to be very useful and I'm happy to concede that RF projects are beyond my skill levels.
I don't think there was any mention of RF in this thread? For an oscilloscope you really need about 10x sample rate to the maximum frequency of interest. So your 96kHz audio codec is only really useful for observing signals upto around 10kHz. Beyond that you're likely not capturing enough information to visualise the waveform to a useful degree of resolution.
The fact that there are commercial products like the DSO Nano seems to imply that I'm not alone. I doubt many home hobbyists could afford (or need) the audio analyser you mentioned.
That's not the point. I agree most hobbyists don't need an audio analyser. But a decent scope is essential. A poor quality scope just lies to you. Certainly at A-level I would expect students to understand the limitations of the equipment they are using, and understand measurement uncertainties, etc.
Google for "site:raspberrypi.org oscilloscope" to see the forum post that I was referring to.
Thanks for the link. It looks like the summary is: doing it properly is not cheap, might as well by a PICO kit, better to use the RasPi as the GUI and leave the sampling to a scope-grade front-end.
Google for "site:raspberrypi.org wolfson" to see some of the forum posts that discuss the use of well reputed audio chips which are far from low-grade.
I don't see how moving a 24-bit ADC/DAC to an external box at the end of a USB cable makes those 24-bits any better. And it misses the point about latency.
I think I was the one who mentioned Wolfson in that thread The point of an external USB box is that it gives you physical separation between the ADC/DAC and the noisy environment of the CPU.
Why is this important? Lets take your 24-bit converter. As it is designed for audio lets also give it a -10dBV domestic hifi input range (about 890mV peak-to-peak) and lets set this to the full range of the converter to get the most out of it.
I'm sure you can work out the maths yourself, but the result is that the least significant bit corresponds to about 53nV.
Please think about that.
While you do, here's an interesting thought: to get the thermal noise of a 1k0 resistor to below this level you'd need to cool it down to 1 Kelvin.
So unless you're going to cool your electronics down to this level then the intrinsic thermal noise of the electronics will render meaningless the lowest few bits of the converter. You could use a 20-bit converter and still be at the thermal noise level of that 1k0 resistor. Add in the rest of the circuit and you'll likely lose another couple of bits in noise. Now we're down to 18 bits.
For a scope, the vertical resolution is not that important. What matters more is the sample rate. High-end scopes don't go much above 12 bits as there's little point. They're more interested in high sample rates and accurate timing.
Oh, that's another thing. In the noise budget we also need to include the noise from the clock source that drives the timing signals that tell the the ADC when to sample the input. Any noise here (jitter, phase noise, etc) will manifest itself as yet another noise source.
Besides, where is the educational value in just buying a ready made product?
What, like a RasPi? Sure, a few students will find it useful to design and build a codec interface, but the majority will find it far more useful to use a ready made product so they can get on with what they want to do.
It can also be a great education understanding the limitations of the equipment, how to design experiments within those limitations, and interpretting the results given the limitations of the equipment. Its an excellent way to teach precision, accuracy, uncertainty, probability, random processes, etc. If you have to build the interface yourself you can very quickly get bogged down in minutiae detail and generally tedious engineering issues that distract the students from their real projects.
(If the goal is to design a codec or scope interface then of course they would be looking at understanding codec datasheets, how to layout the PCB to minimise noise, codec imperfections like INL and DNL and so on, plus low-noise circuit design, EMC/RFI shielding, etc).
If you were to open a comparable USB audio device you'd find some analogue stuff, some power stuff, USB stuff, ADC, DAC, micro-controller and perhaps some memory. Most of which is in the RPi so how can a comparable design based on the RPi be significantly worse? The only difference is the plastic box.
And the PCB layout. And the choice of surrounding components. And the quality of ADC. And many other factors. That's why, for example, the USB scopes from Pico Tech have significantly different feature sets and prices compared to USB audio interfaces.
But this is getting rather off the topic of an audio interface. I would suggest that for the relatively small number of people who need something approaching a decent audio interface to the RasPi that they investigate USB audio interfaces. And anyone who wants to experiment with low-level ADCs and DACs get an Arduino and build R2R ladders for themselves and bit bang the pins. After all, this is all about education, of which the RasPi board is just one means of achieving that aim.