Monthly Archives: January 2012

#oggstreamer – Having fun with non-intrusive debugging

Hi out there – I found the problem with the buzzing noise, there was a short on the VDD_Analog and RCAP Pins on the LQFP Package of the VS1063. Now the thing sounds quite decent. It still needs some fine tuning. Help for this is on the Way, I will meet an Audio Engineer probably next week.

Meanwhile I put together the device to see if there are any mechanical problems – but Verficiation in 3D (with SketchUp) paid off and no problems when assembling the device – well there are some minor issues with the housing but those are basically translation errors to the punching machine.

And to see how the VS1063 performs with various bitrate settings I added support for statistics to the STM8 Firmware. With the help of the STM Studio Tool which allows non-intrusive debugging it is now possible to monitor the bitrate and buffer status in realtime. The bitrate shows the average bitrate in the last 1/4 second – whereas the buffer status shows more or less random the current bufferstatus – because the update rate via the STM-Link is limited.

Run 1: CBR Mode with 128000 bps

This shows that we have some Peaks with around 170000 bps and average around 130000bps.

Run 2: Quality Mode with q=10

Bitrate varies between 250000 and 400000 bps

Run 3: Quality Mode with q=1

Bitrate varies between 0 and 135000 bps

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#oggstreamer – first recording + NOISE

Well the OggStreamer is working … basically. I recorded today samples of classical music and it turned out that there is a problem with background noise. If you want to listen you can download the sample here

would have been to easy … i guess 😦

#oggstreamer – measuring the input amplifier in detail

The input amplifier is now designed to roughly cover a range from -20dB to +20dB, which translates to an amplitude amplification of x0.1 to x10

Today the frequency response of the ampilifier using a standard PC-Soundcard and the Shareware Version of the audioTester Software. This is far from an accurate measurement but it gives me quite a good hint that we are on the right way. I already noticed before that the output of my PC-Soundcard is slightly unbalanced and this can be seen again in this measurement. I also want to note that I measured the frequency response of the Soundcard only as well and used the result as calibration data for the actual measurement.

With +20dB gain the frequency response looks like this (with groundlift activated)

Without groundlift (here we short the input Capacitors on the Ground line C24 and C28)  The spike on the left is unclear why but maybe due to an error in calibration data.

Results: In +20dB gain Mode we see a drop in gain at around 16kHz. Groundlift does not really effect the frequency response in the audible spectrum.

With -20dB gain the frequency response looks like this (with groundlift activated):

And without groundlift:

Results: with -20dB gain we see an unbalanced Situation with groundlift activated. And we further see an steady increase in gain at around 6 to 7 kHz.

In overall the Results look acceptable – I also ran an online radio station through the input amplifier today and listened to music and the Music sounded nice – it sounded a tick more crispier when ran through the input amp.

Together with Michi we will use a professional audio analyzer to do the measurements in the next weeks

#oggstreamer – bugtracking hard- and software issues

Michi – The Hardware developer just visited me and we had a talk about the issues i have found on the PCB. He told me about Bugtrackingsystems he is using for other projects. Thats why we started to use the built in Ticketingsystem in Sourceforge to keep Track of both Hardware and Software Bugs found on the OggStreamer. if you are interessted have a look at the Ticket-Section @ Sourceforge

#oggstreamer – measuring power supply and input amplifier

Today I noticed that I can’t put every project progress on the Blog – so I started to use the WIKI more. Nevertheless – in my opinion – it is really important to check the power supply rails of your design. So I decided to put this on the Blog. I measured the power lines and all the corresponding ripple voltages – and it looks quite good. I measured the ripple by using the “AC Coupling”-Mode on the oscilloscope. And I added the pictures together – so in the pictures on top you’ll see “DC”-View and on the bottom the “AC”-View. I also used some kind of precision probe (a salvaged spring from an old printer) – to keep the ground line short – so that I don’t measure something else than the actual ripple: (sorry for the bad foto quality but I only have my cell phone at hand at the moment)

All the measurements were done while the OggStreamer was connected to a PC Sound card playing 440Hz with an amplitude of about 0,5V-PP and ogg encoding enabled.

  • 5V Main-Power Supply measured @ C78:

I am using a 5V-wall power supply from Schukat (Order Number: HNP06-050) Click here for the Datasheet. Specs say typical 100mV-PP ripple. I measured about 50mV-PP ripple.

  • 5V OPV-Supply measuered @ C18

The measured ripple is around 32mV which is not to much. Also considering the the used OPA LME49721 has a excellent Power Supply Ripple Rejection (PSRR) of 103 dB. The measured ripple has a frequency from about 45 Hz – I don’t know were this comes from – maybe it is the main line – but anyhow the ripple is  negligible.

  • 3V3 Digital Supply measured @ C56

Everything is fine here – Ripple is about 25mV-PP

  • 1V8 Digital Supply measured @ C71

Everything is fine here – Ripple is very low around 6mV-PP

  • 3V3 Analog Supply measured @ C10

The VS1063 has uses a separate Analogue Supply  Voltage. It could be tied together with the 3V3 digital supply, but in our design we decided to seperate those two rails be an small coil to block high frequency noise. The pcb layout guidlines for  VS10xx are stating, that you should tie them together directly – So maybe the coil ferrite bead (I got confused and mixed coils and ferrite beads up) will be replaced by a zero-Ohm bridge. The VS1063 is said to have a decent PSRR as well, although I can’t find the numbers in the Datasheet. The measured 35mV-PP should be OK.

Next I also measured the input amplifier. The input amplifier for the OggStreamer is an inverting OPA designed to be capable of amplifying or to attenuate the signal as needed. The gain is designed to range from 0.1 to 11, which translates to about plus/minus 20dB.

    • 440Hz Signal measured before the OPA @ C25 (left) and C32 (right)

Left is 286mV-PP and Right is 288mV-PP

    • 440Hz Signal measured after the OPA – in amplifier mode (x10) @ C20 (left) and C4 (right)

Left is 2.5V-PP and Right is 2.56mV-PP

    • 440Hz Signal measured after the OPA – in attenuator mode (x0.1) @ C20 (left) and C4 (right)

Left is 30mV-PP and Right is 32mV-PP

It seems like the output of the PC-Soundcard is slightly unbalanced. Doing the math the OPA circuit has a gain from 0,105 to 8,74 – which is almost 0,1 – 11 as designed. I want to note that  I am currently using standard 0805 Resistors for the OPA, which will be replaced by Mini-Melfs metal-film resistors in future. The values for the Restors are 1k for R13 and R35 and 10k for R7 and R30 – this means that the Input load is about 1k.

#oggstreamer – Amanda Wozinak: open-sourcing the engineering processs

Today i listened to a brilliant talk from Amanda Wozinak, which she held on the 28C3 congress. The slides can be downloaded here. I find it really inspiring to understand engeneering as a process and that documenting your stuff really pays off on the mid/long run.

w0z also laid out some initial questions, which should be asked when starting a development – well, the OggStreamer has already started but I am somehow in the mood to answer this questions now.

1. Why are we making this?

  • Admiration for the parts, especially the AudioDSP and the Lantronix XPortPro.
  • Scoring at the Lantronix XPortPro DesignContest (done 😉 )
  • Building something useful our local radiostation
  • Just fur Fun
  • Building something to present as a product made in the Open Technology Labratory

2. Who is this for?

  • mainly for Radio Stations

3. How will this be used?

  • Connecting remote studios to the main studio
  • Connecting Live Events to the main studio
  • Connecting the main studio to remote transmitters
  • Providing an gateway for Analog-Audio to the Internet (like http://locusonus.org/)

4. What features does it need to have (now)?

  • Converting and compressing analogue audio to ogg/vorbis
  • upstreaming the ogg/vorbis to an (external) IceCast2 Server
  • Feeding an internal Icecast2 Server (for a small number of listeners)
  • Adjustable Input Volume and VU Meter
  • monitoring the incoming signal with Headphones
  • configure quality and server settings via ssh
  • Firmware Update for XPortPro
  • internal web server with small streaming applet

5. What features does it need to have (later)?

  • Configuration Web Interface
  • Firmware update of STM8 Microcontroller
  • Talkback channel from Studio Operator
  • optional mp3 support and other streaming formats

6. What are the legacy requirements?

  • IceCast2 Support

7. Who’s going to build this?

  • PCB – WEdirekt
  • SMD assembly – abatec
  • THT soldering by hand
  • Lightguids – 3D printed from The Open Technology Labratory
  • mechanical works/Housing – from the professional school Attnang
  • final assembly @ The Open Technology Labratory

8. How many do we want to make?

  • 1 breadboard-Prototyp is already built
  • the next Prototype to test the PCBs is soldered and now tested
  • 12 pcs. will be manufactured – once the PCB-prototype is debugged and tested
  • if there is demand we will make another batch of around 10-30 pcs. this year

9. What is the budget?

  •  I personally invested a whole lot of time and around 2000 EUR in this project
  • This project heavily relies on friends that support me with various issues: like PCB design, mechanical works, EMI considerations, product design, Audio Design, …
  • with out the help of all this generous supporters it would take another 3000-4000 EUR to produce the first 12 devices.
  • If this project would be developed by an electronics solutions company I estimate that such a product would be in the range of 20000-40000 EUR

10. What is the timeline?

  • check timeline here – but as i found some bugs on the PCB and I want to invest more time into testing – I think this plan will delay for about a month.

Blog statistics Q4 2011

here are the wordpress stats for 2011 – just for your Info the Blog was put in place only in late Oct 2011 so this statistics only cover about 2 month 😉

The WordPress.com stats helper monkeys prepared a 2011 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 2,700 times in 2011. If it were a cable car, it would take about 45 trips to carry that many people.

Click here to see the complete report.