Engines, mono patches and overload issues

Zynthianic Sounds
1

To the experienced sound and synth magicians: Sorry for beginner’s questions, I am sure it must have been discussed here several times (or everyone else just knows?), but I cannot find anything…

While experimenting mainly with the HW and UI, I almost forget to explore all the different sound engines and then I am a bit surprised and confused:

  • I noticed many patches (e.g. in Odin2, Obxd, sometimes in SurgeXT) only produce sound into the left channel; I can understand they are probably mono patches, but why do they not just play equally into both the left and right channel then? the Digital Audio Peak Meter indicates equal sound intensity in both channels, but I only seem to hear sound from one channel

  • some patches (especially in SurgeXT) cause overload very quickly (heart symbol getting red or even turning into red triangle, while the sound gets lost completely) - I have surely seen this mentioned somewhere, I am just surprised it still happens that easily with the Pi5 as well (are those patches really that complex? I thought Pianoteq was one of the most computationally complex engines…) - and I am also a bit surprised I cannot see any high load indication in the “good, old” htop utility in the terminal (maybe the overload is just too sudden/momentary?)

Thanks in advance for all explanations.

2

Oops! The first issue seems to be a HW bug. It does not happen with other sound cards! Going to check the I2S wiring of the Hifiberry.

3

I can believe that Surge can have a higher load than Pianoteq in certain circumstances. Pianoteq devs put in a lot of work to make the engine work on a pi3. Surge we’re just grabbing the code and compiling it for arm. Also some surge presets will have lots of sustained complex layered waveforms. Whereas pianoteq is mostly just going “thunk” in a very clever and appealing way.

4

The source of issue no. 1 located: it’s neither wiring, nor zynthian nor the hifiberry. It’s the little cheap amplifier module (TPA6132) I use to connect headphones to the hifiberry. Obviously, it does some “smart” (differential?) channel mixing of its own:

When playing left channel only, I can hear it from both left and right speaker. When playing right channel only, I can hear it from the right speaker only. Wonder how it makes sound from left speaker only … maybe when both channels play equal signal? Have to test that hypothesis.

OMG, can’t I just get a simple stupid two channel headphone amplifier module for embedding, please?

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5

Right. It seems to be really even worse on a Pi4!

I can probably hear those layers in some of the patches. But others seem rather simple for an unexperienced ear. Maybe they are not.

I haven’t thought of the software just missing optimizations. Thanks for explanation.

6

Guess what? The problem wasn’t in the amplifier, though. It can actually be deduced from the description above. First prize to the first one who can guess the real cause! Hint: it is probably the most trivial and stupid mistake you could think of.

7

Your ears were on backwards?

Maybe a phase wiring issue?

8

Here’s a nice simple one, and the schematic is even under a creative commons license:

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9

Wiring of the phone jack: confused left channel and ground contact pins! And, voilà, suddenly you have a “magical” differential disbalance that looks like a very sophisticated and complex issue. Such a stupid nonsense!

That’s like spending a whole day debugging all your application modules and components just to find out a stupid typo in the name of some variable (or a “missing semicolon”) that you just kept overlooking all the time.

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10

At school I was fixing an amplifier that wasn’t working and I just couldn’t understand why the signal just kept getting smaller and smaller as I Worked throu’ the signal chain. Three days of doing this.
I then looked at the transformer voltage selector and realised it was plugged into a socket that wasn’t actually connected because I thought that was a clever way of turning it off and had, inevitably forgotten I’d done this. Amplifiers don’t amplify if they don’t have supply rail voltages.

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