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    If you need low latency (as I always do for live...

    If you need low latency (as I always do for live sound) but are sourcing data from a variable time dependent source such as a PC, the usual way is once you've written to the buffer, if the buffer is...
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    Not my job to teach you things. Get yourself a...

    Not my job to teach you things. Get yourself a programmable signal generator, a mixer and some decent loudspeakers and try it yourself. You'll learn far more than by reading papers or datasheets. ...
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    This was done in the Soundcraft R&D department...

    This was done in the Soundcraft R&D department where I was Engineering Director at the time. We were far too busy designing new products to compete with Yamaha to have time to publish papers so...
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    Please post a link - I've an unused Teensy4 here...

    Please post a link - I've an unused Teensy4 here I'll give it a go with if I've time.
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    Agreed. We were using 112dB AKM devices and...

    Agreed. We were using 112dB AKM devices and information about 12dB lower can be discerned. In fact if you use pure tones you can hear about another 6dB but that isn't a measure of anything useful. ...
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    Just because something has a 96dB noise floor...

    Just because something has a 96dB noise floor doesn't mean that 16 bits is enough - this is the nonsense that led Philips and Sony to think 16 bits was enough for CDs. The ear can pick out a lot of...
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    If it works and you're happy for anybody to use...

    If it works and you're happy for anybody to use your code then doesn't really matter if it's in the library or not - just publish it on Github and know that everyone is grateful that SPDIF is at last...
  8. As well as a hard limiter as Jarkkol suggests, it...

    As well as a hard limiter as Jarkkol suggests, it is usually better to include a softer compression system on the output as well so that the limiter only operates once. Getting the compression law...
  9. If you're a beginner it's always best to build...

    If you're a beginner it's always best to build someone else's design first.
    Google for existing projects such as
    https://www.pjrc.com/polymod-polyphonic-digital-modular-synth/...
  10. You do indeed cross mix reverbs. You often also...

    You do indeed cross mix reverbs. You often also use anti-phase additions to give the reverb extra width.
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    You don't state what bandwidth you need between...

    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...
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    Rather than using a single FFT, you might like to...

    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...
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    Sorry - I only use the Teensys as I/O processors.

    Sorry - I only use the Teensys as I/O processors.
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    I totally agree - getting the maths right is far...

    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...
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    Yes I was assuming filtering before you get to...

    Yes I was assuming filtering before you get to the NE5532s. They are there as output drivers.
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    I think most things are at least 64 bit integer...

    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...
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    Figure 1 in the link Sin-Phi gave is fine, only...

    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.
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    There's only one good way for polysynths - a 32...

    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...
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    From Paul himself last month : There is...

    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...
  20. The Teensy 4.0 has far more horsepower for...

    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...
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    Thanks Paul. That's a pity. Looks like I'm...

    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...
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    Not quite - to sound the same as most analogue...

    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...
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    The Teensy 4.0 chip supports SPDIF which is...

    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.
    ...
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    I'm afraid I read it as SAI1 offers 8 in, 2out...

    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...
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    Thanks Richard Those links are very useful. ...

    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...
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    Yes about 95% gets through okay, but when they...

    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...
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    Careful if anybody is ordering these to the UK as...

    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...
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    Thanks Richard All studios just distribute a...

    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...
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    In the first case, the data setup time of 15nS...

    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...
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    Not that I use it, but I'm pretty sure you'll...

    Not that I use it, but I'm pretty sure you'll find PulseAudio does work ok on a Pi nowadays.
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    Using Teensy4.0 with external word clock

    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...
  32. In the old days many people used to use roller...

    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...
  33. I agree 3.3V should be generated on-board using...

    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.
  34. The crunchyness is possibly caused by just as...

    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...
  35. Teensy is at the top, with a Pi4 in the middle. ...

    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...
  36. Almost snap ! 1*SPI, 2*I2S, 1*SPDIF Doesn't...

    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 !
    ...
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    Thanks Paul. As I suspected you have used...

    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...
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    Whilst I didn't report the problem, I have seen...

    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...
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    Is there source code somewhere for the audio...

    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...
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    Well I'm going to have to fix it come what may as...

    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...
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    The CODEC and I2S are fine. The problem is the...

    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...
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    That's a common problem in all digital audio...

    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.
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    Yes I was assuming good PCB design. Resistors on...

    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...
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    The other interfaces aren't as critical as in...

    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. ...
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    Try unplugging everything else using USB on the...

    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...
  46. Another rather expensive alternative is the...

    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...
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    Any plans for a larger Teensy4.5/6 later like the...

    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.
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    I hadn't read the datasheet yet (my Teensy hasn't...

    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 !
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    My Teensy4 hasn't arrived yet, but I've been...

    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...
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    http://www.dspguide.com You can't beat the...

    http://www.dspguide.com

    You can't beat the price !! And the quality is there as well.
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