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  • MikeDB's Avatar
    09-09-2019, 01:37 PM
    In the old days many people used to use roller ball microswitches such as these https://uk.rs-online.com/web/p/microswitches/1854073/ They are break before make so you can time between them and calculate the...
    11 replies | 125 view(s)
  • MikeDB's Avatar
    09-05-2019, 08:16 PM
    I agree 3.3V should be generated on-board using an LDO, but doing it from +12v is a bit extreme. Adding +5V to the connector seems a good idea to me, and something I always do.
    9 replies | 313 view(s)
  • MikeDB's Avatar
    09-02-2019, 11:19 AM
    The crunchyness is possibly caused by just as little as one sample going too high (positive or negative) and wrapping round. Once this gets into any filter the filter usually gets confused and struggles to recover. ...
    20 replies | 1661 view(s)
  • MikeDB's Avatar
    09-01-2019, 02:39 AM
    Teensy is at the top, with a Pi4 in the middle. Pi4 doesn't do SPDIF and only has one I2S so the Teensy connects via SPI to expand it. I'm not aware of any standard I2S connector pinouts - I use my own which you can...
    9 replies | 313 view(s)
  • MikeDB's Avatar
    08-31-2019, 07:33 PM
    Almost snap ! 1*SPI, 2*I2S, 1*SPDIF Doesn't use the MQS pins for which the word Medium Quality is almost fails the Trade Descriptions Act - a better term would be AM Medium Wave Quality !
    9 replies | 313 view(s)
  • MikeDB's Avatar
    08-28-2019, 10:32 AM
    Thanks Paul. As I suspected you have used separate left and right buffers. I haven't dug into the code yet to see if that's definitely the problem, but I've always found having a single buffer with left in 0,2,4.......
    16 replies | 226 view(s)
  • MikeDB's Avatar
    08-28-2019, 07:55 AM
    Whilst I didn't report the problem, I have seen the same effect if the audio driver uses separate FIFOs for left and right. The sync signal gets delayed slightly between generation and output and the DAC driver takes...
    16 replies | 226 view(s)
  • MikeDB's Avatar
    08-27-2019, 09:17 PM
    Is there source code somewhere for the audio drivers ? Point me to it and I'll see if there's an obvious fix. Otherwise I'll be writing my own (which I may do anyway as somebody said it has 2.2mS of latency due to it...
    16 replies | 226 view(s)
  • MikeDB's Avatar
    08-27-2019, 09:12 PM
    Well I'm going to have to fix it come what may as I have a blank PCB for a Pi4, a T4 and several 5102 DACs arriving from China any day now. The T4 adds SPDIF and extends the Pi's limited I2S capabilities. It's just...
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-25-2019, 10:24 PM
    The CODEC and I2S are fine. The problem is the software module generating the audio signal is usually decoupled from the I2S interface, often by driver code which includes a buffer. As you point out, sometimes it...
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-25-2019, 07:25 PM
    That's a common problem in all digital audio applications and not restricted to Teensy or I2S. You need to sync to a master timecode to overcome it.
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-20-2019, 12:23 PM
    Yes I was assuming good PCB design. Resistors on all tracks (or configuring the internal ones on STM MCUs) right near the source (which remember is at the other end sometimes !) is always best, but if you don't have...
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-20-2019, 08:49 AM
    The other interfaces aren't as critical as in this case they are all just allowed to settle and then clocked in by MCLK so it is this line that it is essential there are no reflections. STMicroelectronics MCUs have...
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-18-2019, 02:06 AM
    MikeDB replied to a thread USB midi issues. in Audio Projects
    Try unplugging everything else using USB on the PC. Hard I know as that includes the mouse and keyboard, but my guess is that something is transmitting constantly whereas on a laptop most things are internal.
    10 replies | 333 view(s)
  • MikeDB's Avatar
    08-17-2019, 01:23 PM
    Another rather expensive alternative is the CY15B104Q: 4-Mbit (512 K 8) Serial (SPI) F-RAM. It's in a slightly different 8 pin package and haven't checked the actual pinout, but will give you 4 times the length as...
    27 replies | 5856 view(s)
  • MikeDB's Avatar
    08-16-2019, 12:19 PM
    Any plans for a larger Teensy4.5/6 later like the 3.5/6 to overcome the pinouts issue ? I suspect a lot of people may prefer that for such a powerful processor.
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-16-2019, 11:00 AM
    I hadn't read the datasheet yet (my Teensy hasn't even arrived) but if you are saying that OUT2/3/4 can be made into inputs that's fantastic news. A small complete digital mixer on a Teensy !
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-16-2019, 09:04 AM
    My Teensy4 hasn't arrived yet, but I've been assuming the use of OUT1A, OUT1B, OUT1C and OUT1D together with MCLK1, BCLK1 and LRCLK1 wukk give a standard 4 channel I2S. I wasn't going to use OUT2 or it's MCLK and other...
    68 replies | 3868 view(s)
  • MikeDB's Avatar
    08-14-2019, 11:59 PM
    http://www.dspguide.com You can't beat the price !! And the quality is there as well.
    7 replies | 370 view(s)
  • MikeDB's Avatar
    08-14-2019, 09:45 PM
    Ok took me a while but try this. It won't be absolutely correct but should give you a strategy. For k=1 calculate phaseadjust as you are doing so you need a starting cos() and sin() values. Now if you rewrite the...
    12 replies | 660 view(s)
  • MikeDB's Avatar
    08-14-2019, 01:25 PM
    Fair enough, but the OP did ask about running something far more complicated, probably using the Wavelet transform. The Teensy4.0 should be more than powerful enough for what you are doing and hopefully you'll get...
    12 replies | 660 view(s)
  • MikeDB's Avatar
    08-14-2019, 10:17 AM
    Yeah I've been interested in audio for about fifty years and was at Soundcraft for a time 20 years ago. Now I design stuff on contract but have been thinking about doing my own brand. Being DSP agnostic is good. ...
    12 replies | 660 view(s)
  • MikeDB's Avatar
    08-14-2019, 04:07 AM
    Hi Jay. Yes the Pi is used for real time audio. Two cores run Linux. I try to make one do all general housekeeping whilst the other focuses on input control - MIDI, HID, etc. The other two cores are (supposedly)...
    12 replies | 660 view(s)
  • MikeDB's Avatar
    08-13-2019, 09:17 PM
    Great thanks. I assumed they would be /Program and /Off but it would have helped if it was documented somewhere.
    4 replies | 229 view(s)
  • MikeDB's Avatar
    08-13-2019, 08:32 PM
    I've ordered a Teensy 4.0 which will arrive in a couple of weeks but am designing a PCB to put it on already. But I've failed to find anything in the documentation online saying which way up the Program and On/Off...
    4 replies | 229 view(s)
  • MikeDB's Avatar
    08-13-2019, 08:28 PM
    Whilst the Teensy 4.0 is powerful, having tried something similar on an STM32H750 which is of similar performance, I think you will struggle. I've migrated to a Pi4 for high powered audio processing.
    12 replies | 660 view(s)
  • MikeDB's Avatar
    08-13-2019, 08:24 PM
    I really wouldn't bother with the MQSL/R pins. A new definition of 'Medium Quality Audio' from NXP I'm afraid. Cheapest solution is probably to buy one of those $1 USB audio dongles and then rip off the USB - there's...
    8 replies | 447 view(s)
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