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  • MikeDB's Avatar
    10-11-2019, 03:36 AM
    You don't state what bandwidth you need between each node, but if not too high one possibility would be to make a mesh of Teensy4.0s using the I2S ports, with IN1, OUT1A, OUT1C, OUT1D, IN2 and OUT2 reprogrammed as...
    8 replies | 277 view(s)
  • MikeDB's Avatar
    09-29-2019, 02:55 PM
    Rather than using a single FFT, you might like to consider using the lower portions of multiple FFTs. The low frequencies would be based on possibly the last one second of audio input, but for higher frequencies you...
    63 replies | 10998 view(s)
  • MikeDB's Avatar
    09-28-2019, 09:05 PM
    Sorry - I only use the Teensys as I/O processors.
    29 replies | 1318 view(s)
  • MikeDB's Avatar
    09-28-2019, 08:00 PM
    I totally agree - getting the maths right is far more important than optimising the odd instruction out of the code. And when I want autotune, I start with wavelets, not short FFTs as selecting the correct algorithm...
    29 replies | 1318 view(s)
  • MikeDB's Avatar
    09-28-2019, 12:29 PM
    Yes I was assuming filtering before you get to the NE5532s. They are there as output drivers.
    5 replies | 122 view(s)
  • MikeDB's Avatar
    09-27-2019, 09:12 PM
    I think most things are at least 64 bit integer internally nowadays - ARM 64 bit processors are so cheap that using anything else is silly. Some use 80 bit floating point, most notably PC based apps.
    6 replies | 115 view(s)
  • MikeDB's Avatar
    09-27-2019, 09:03 PM
    Figure 1 in the link Sin-Phi gave is fine, only use NE5532s and the correct value of output resistors (300 Ohm?) for your application.
    5 replies | 122 view(s)
  • MikeDB's Avatar
    09-27-2019, 08:48 PM
    There's only one good way for polysynths - a 32 bit DAC and run the signals at about 24 bits which still gives a good signal to noise ratio. Yes I realise 32 bit DACs aren't really 32 bits because of their noise floor,...
    6 replies | 115 view(s)
  • MikeDB's Avatar
    09-26-2019, 12:33 AM
    MikeDB replied to a thread Audio over Serial in Audio Projects
    From Paul himself last month : There is the small matter of (so far) no software support for Teensy 4.0's S/PDIF peripheral in the audio library. Given the power of the Teensy4.0 for audio, I wouldn't think...
    4 replies | 110 view(s)
  • MikeDB's Avatar
    09-25-2019, 08:16 PM
    The Teensy 4.0 has far more horsepower for synthesis and any I2S->audio card can be patched onto the output pins so no need to stay with the one suggested. Loads on Aliexpress and elsewhere. My personal preference is...
    7 replies | 254 view(s)
  • MikeDB's Avatar
    09-25-2019, 07:10 PM
    Thanks Paul. That's a pity. Looks like I'm back to the STM32H7 MCU series then as that can multiply the LRCLK by up to 256 with extremely low jitter - but is an absolute PITA with dreadful support :-( I'd assumed...
    9 replies | 229 view(s)
  • MikeDB's Avatar
    09-25-2019, 06:47 PM
    Not quite - to sound the same as most analogue ones you want to sweep them up and down with equal logarithmic spacing. Still easy to do, just choose the ratio you want and then multiply the base notch frequency by...
    4 replies | 94 view(s)
  • MikeDB's Avatar
    09-25-2019, 06:43 PM
    MikeDB replied to a thread Audio over Serial in Audio Projects
    The Teensy 4.0 chip supports SPDIF which is exactly what you want for point to point as that is what it was designed for. But I believe you'd have to write your own drivers for now for the Teensy. The second...
    4 replies | 110 view(s)
  • MikeDB's Avatar
    09-23-2019, 08:40 PM
    I'm afraid I read it as SAI1 offers 8 in, 2out through to 2 in, 8 out, i.e. 10 channels in total, not 16. But I think you can have these at 384kHz if you want. But you can use the SAI2 for another 2 in and 2 out and...
    22 replies | 480 view(s)
  • MikeDB's Avatar
    09-23-2019, 01:06 PM
    Thanks Richard Those links are very useful. Will try the tool and see if it does what I want. Given there are so many PLLs in the Teensy MCU I was hoping not to add an external one, but that's always a possibility....
    9 replies | 229 view(s)
  • MikeDB's Avatar
    09-22-2019, 12:55 PM
    Yes about 95% gets through okay, but when they charge you it hurts. I don't mind the VAT but their 'handling charge' strikes me as excessive. I also had an argument with customs over something that shouldn't be...
    25 replies | 1446 view(s)
  • MikeDB's Avatar
    09-21-2019, 11:52 PM
    Careful if anybody is ordering these to the UK as even a single unit exceeds the 15 product + postage customs limit and so could incur VAT plus a 10 mail handling fee. It's pot luck whether this gets applied or not,...
    25 replies | 1446 view(s)
  • MikeDB's Avatar
    09-21-2019, 12:36 AM
    Thanks Richard All studios just distribute a 96kHz (or 192/384 if you've a lot of hard discs you want to fill up :-) clock to sync everything. Sending MCLK everywhere would be a nightmare and wouldn't actually...
    9 replies | 229 view(s)
  • MikeDB's Avatar
    09-21-2019, 12:03 AM
    In the first case, the data setup time of 15nS makes this unlikely to work as you are thinking. In fact SAI1 outputs 8 channels as 4 streams of 2 channels over the 4 active outputs (or active inputs if you prefer) so...
    22 replies | 480 view(s)
  • MikeDB's Avatar
    09-20-2019, 11:56 PM
    Not that I use it, but I'm pretty sure you'll find PulseAudio does work ok on a Pi nowadays.
    22 replies | 480 view(s)
  • MikeDB's Avatar
    09-20-2019, 04:18 PM
    I want to supply the Teensy just with the studio Master Clock (96kHz in our case) and have it generate it's own I2S LRCLK and BCLK (and MCLK if possible) from it. I've read through the whole iMXRT Reference Manual but...
    9 replies | 229 view(s)
  • 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...
    12 replies | 201 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 | 531 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 | 1759 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 | 531 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 | 531 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 | 298 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 | 298 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 | 298 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...
    71 replies | 5188 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...
    71 replies | 5188 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.
    71 replies | 5188 view(s)
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