ruffrecords

Raspberry Pi
« on: August 18, 2012, 05:10:35 PM »
Anyone here have any experience of this platform? I was wondering, with its built in graphics and floating point and OS, whether it might be a good candidate for the basis of a general audio test set.

Any views?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


Twenty Log

Re: Raspberry Pi
« Reply #1 on: August 19, 2012, 01:46:56 AM »
I remember looking at it awhile ago.   I did not have warm fuzzies for sourcing multiples for a bare metal Pcb build (I needed to control several hundred relays and perform FFTs whilst maintaining Ethernet/web server connectivity and such in different projects)

I will say that these embedded things can sometimes be dodgy. For example I invested in the DIGI connect ME which is a simple ethernet metal box/ "can" style package with an ARM that had the "OS" or "RTOS" to do some basic web stuff such that you can for example monitor an appliance by tickling some pins on the can package and translate it to Ethernet/web...  SPI was available at the limited exposed pins/ port on this can but the SPI CLOCK was kept internal to the can for dumb reasons. $1500 for no SPI. sheeesh. 

But with the cost of raspberry pi maybe not an issue here.

Maybe the platform has been maturized since I looked at it.

I ultimately ended up with Analog Devices blackfin DSP running Linux as the OS was pretty standardized and had all the Ethernet, web, video drivers, SPI etc.   But not for the faint of heart especially if you have a 64 bit Windows OS as it breaks the development kit norms and one actually has to think outside of any instructions.

ruffrecords

Re: Raspberry Pi
« Reply #2 on: August 19, 2012, 06:15:56 PM »
One of the main reason I was interested in the Rasberry PI is that it runs Linux as standard.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Twenty Log

Re: Raspberry Pi
« Reply #3 on: August 19, 2012, 09:28:27 PM »
Indeed...  Linux is a good way to go...  However I have not been able to find a distributor for the BCM2835 system on chip CPU/GPU from Broadcom that the raspberry pi uses, as I would need a bare metal, from the ground up, spin my own PCB custom form factor...

 I needed to have 160+ chip selects thus an FPGA, and did not need the camera or video input stuff....

For purposes you propose I suppose that the pi platform would be good especially at the price point. For comparison the blackfin eval was something like $229 +/-....  Both way better and more functional than other things like DIGI connect me.

The main Linux issues I ran into was that my host system is 64 bit. Windows..  The embedded Linux DEVELOPMENT environment for the blackfin (gnu tool chain and CoLinux examples in the documentation) are somewhat moot in that CoLinux cannot run (at this time) on a 64 bit host system... So I have VirtualBox running ubuntu in a window on my Windows host as the host system for cross compiling.  A lot patching and updating, manual configuration, google searches, (Oxford Comma) et cetera...  The blackfin embedded Linux needs a Linux host for cross compiling of course.

I dunno if there are similar paradigms/issues on the pi?

ruffrecords

Re: Raspberry Pi
« Reply #4 on: August 20, 2012, 04:59:48 AM »
I see your problem with 64 bit Widows development platform. Fortunately mine would be 64 bit Linux so it should be somewhat more straightforward. As you mention, the Pi is extremely cheap so I must just get one to try it out. Thanks for you input.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Twenty Log

Re: Raspberry Pi
« Reply #5 on: August 20, 2012, 08:28:52 AM »
Nice!  Yes, these embedded kits sometimes have "surprises" and occasionally a show stopper that are not evident unless a lot of up front research...  and even then not exposed until invested in the kit since some of them do not include schematics without buying the kit...

The risk with the pi seems mitigated relatively speaking with price.  Worst case it is an expensive door stop ;)

audiomixer

Re: Raspberry Pi
« Reply #6 on: August 20, 2012, 03:33:41 PM »
Just wondering,

what would your application be?

- Michael


ruffrecords

Re: Raspberry Pi
« Reply #7 on: August 20, 2012, 04:29:35 PM »
Just wondering,

what would your application be?

- Michael

As I mentioned in the first post I was thinking of a general audio test set. It would need some external hardware to provide balanced ins and outs but once the data is captured the there's no limit to what can be done with it.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Twenty Log

Re: Raspberry Pi
« Reply #8 on: August 20, 2012, 07:18:49 PM »
I just looked at the wikipedia page again. I didn't see any I2S for A/D.

Maybe I misread?

I dunno.  I believe everything I read on the Internet......   First I post it to this forum, then I read it, then I _believe_ it ;)

Perhaps a USB A/D D/A?  Drivers?

But I also saw note 4 saying that the ARM11 processor inside of the BCM2835 was based on version 6 of the ARM family which is "not popular" and old aged (unsupported) for various flavors of Linux ?!?!?!
Thus drivers for the flavor of Linux may be interesting?

Could be one of those surprises but again mitigated by initial price...

audiomixer

Re: Raspberry Pi
« Reply #9 on: August 20, 2012, 07:50:45 PM »
How about audio over ethernet / Dante / AVB / like the xmos design?

you have a plan concerning the software, besides using linux, what application?

- michael


tmuikku

Re: Raspberry Pi
« Reply #10 on: August 21, 2012, 06:16:33 AM »
They have recently released IO board for the raspberryPi http://www.raspberrypi.org/archives/tag/gertboard

It is supposed to have AD / DA conversion, don't know if the performance is anything usefull though..

ruffrecords

Re: Raspberry Pi
« Reply #11 on: August 21, 2012, 06:59:19 AM »
As it stands, the Raspberry Pi audio facilities are primitive - analogue audio out only - no audio in, so some add on board for audio capture at least would be necessary.

In terms of software I was thinking of writing my own. The platform gives you all the graphics capabilities you could wish for and the Python language is a convenient means of accessing them at a reasonably high level.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

12volts

Re: Raspberry Pi
« Reply #12 on: August 21, 2012, 07:07:31 AM »
Anyone here have any experience of this platform? I was wondering, with its built in graphics and floating point and OS, whether it might be a good candidate for the basis of a general audio test set.

Any views?

Cheers

Ian


Here is a photo to whet your appetite Ian. The Raspberry Pi as amazing for the price. £28!  I wont go on about the spec. and the story behind it,
you can get all that via a search engine. Sadly the demand is very high so you either have a long wait or you can only get your hands on one or both.
The board shown has a dual USB port loaded with a wireless keyboard/mouse and a wireless network interface. All these connected without problem.
It has HDMI, Stereo output, A Digital GPIO and Ethernet. Two 'special' headers, one is for a 5m pixel camera due release next early next year, the other
kept quiet. Storage is on an SD card, I had a spare 16G card, but no reason not to have larger or smaller capacity. Choice of the operating system version.
All things considered it is a remarkable device at a jaw dropping price.   
Do it! Buy one now!

The Arduino board is there for comparison.


Frank B

dmlandrum

Re: Raspberry Pi
« Reply #13 on: August 21, 2012, 06:14:24 PM »
I decided to drink from the Kool-Aid and I ordered away for two. I expect to see them in six months or so. The demand has been so high that the makers have not been able to keep up at all.

I do have two projects in mind for them. One is a SID-based polysynth. I was going to do this with an FPGA before, but the R-Pi presents an opportunity to make it a cheaper, easier, and more capable. The networking alone is worth the $35, as that means I can make a programming interface for the synth ("programming" as in making synth patches in this context) that I can just ssh into.

The other... Well, I have this dream of making an FFT-based sampler, where all the sample data is converted to FFT data before loading it on the sampler, then using a DSP to process it as notes are played, and then run through iFFT before the D/A. Based on what I know about FFT, this should be possible. May be someone here will tell me otherwise.

Anyway, that's what I'm thinking. I take on way too many projects.
Darren Landrum

Be comforted that in the face of all aridity and disillusionment
And despite the changing fortunes of time,
There is always a big future in computer maintenance.

ruffrecords

Re: Raspberry Pi
« Reply #14 on: September 01, 2012, 08:54:37 AM »
I decided to drink from the Kool-Aid and I ordered away for two. I expect to see them in six months or so. The demand has been so high that the makers have not been able to keep up at all.

I ordered one earlier this week. It arrived today.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

dmlandrum

Re: Raspberry Pi
« Reply #15 on: September 01, 2012, 10:05:07 AM »
Yeah, they're doing better for sure. Both of mine arrived two days ago.
Darren Landrum

Be comforted that in the face of all aridity and disillusionment
And despite the changing fortunes of time,
There is always a big future in computer maintenance.

ruffrecords

Re: Raspberry Pi
« Reply #16 on: September 01, 2012, 10:47:01 AM »
Got the Raspberry Pi up and running. Sending this message from it!!

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

audiomixer

Re: Raspberry Pi
« Reply #17 on: September 01, 2012, 12:55:03 PM »
that is cool indeed, faster then light [almost]

u care to point out how your measurement system could look like? I would be very interested in a decent priced, high quality measurement setup. I use NTI XL2 and MiniratorPro, but this has limited capability..... and ARTA / RMAA / soundcard has the usual issues with absolute levels....

cheers,

michael

ruffrecords

Re: Raspberry Pi
« Reply #18 on: September 01, 2012, 03:49:40 PM »
that is cool indeed, faster then light [almost]

u care to point out how your measurement system could look like? I would be very interested in a decent priced, high quality measurement setup. I use NTI XL2 and MiniratorPro, but this has limited capability..... and ARTA / RMAA / soundcard has the usual issues with absolute levels....

cheers,

michael

Well, the basic measurements I would like to be able to make are:

1. Frequency response - gain and phase
2. Distortion - THD at any frequency with an optional Fourier analysis, and an intermodulation distortion measurement and also versus output level
3. Noise - to the relevant specs - broad band, quasi peak with various weighting options

As you quite rightly point out, we need to ensure we avoid issues with absolute levels. There are two aspects to this. First the software side, where we need to be confident that any level created or measured by the software is accurate. The good thing about a Linux based system is that we have total control over this.  The second aspect is amplification and attenuation of levels. We need amplification of inputs to better measure noise and of outputs if we want to check our  hardware can cope with say +20dBu. We need attenuation of outputs to provide low level signals for testing things like mic pres and attenuation of inputs to cope with tests at high output levels.  All of these functions I envisage on a separate audio interface PCB controlled by the GPIO ports of the Raspberry Pi.


Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

mhelin

Re: Raspberry Pi
« Reply #19 on: October 19, 2012, 07:31:32 AM »
There is now a new 512 Mb Model B ver. 2.0 version of RPI available (replaced the 256 Mb version) which also includes I2S port on a new header, ordered mine yesterday. See

http://www.element14.com/community/docs/DOC-50776/l/raspberry-pi-model-b-revision-20-512mb-changes?z=VfsSOl

In case you can't read above:

"Additional I/O Expansion
To utilise GPIO signals released by the removal of the version identification links, a new connector site P5 has been added. This carries the four GPIO signals [BCM2835/GPIO28 – BCM2835/GPIO31] named GPIO7 – GPIO10 respectively, along with +5V0, +3V3 and two 0V. Currently this connector is not populated.

This GPIO allocation provides access to one of:

    SDA0, SCL0 (Operating independently of P1 SDA1, SCL1); or
    PCM_CLK, PCM_FS, PCM_DIN, PCM_DOUT or I2S; or
    Four GPIO signals.

This connector is intended to be a suitable attachment point for third-party clock and audio codec boards, and is pinned to be mounted (ideally) on the underside due to connector clash. Pin 1 is marked with the square pad (top left - looking from the top). "

 


 

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