Hiss only after first MIDI played note on 1053

Designing hardware that uses VLSI Solution's devices as slave codecs such as an external MP3 decoder chip for a host microcontroller.
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Davidelvig
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Hiss only after first MIDI played note on 1053

Post by Davidelvig » Tue 2017-07-25 2:31

I have a design on a small PCB driven by a "Teensy" Arduino micro-controller.
RT MIDI setup at startup.
Output through earphone.
Perfect silence after start-up.
I send MIDI notes and they play well.
After any MIDI Note, a hiss starts and persists until reset (reset pin low for 10ms, then high).

I can share the schematic if that's helpful (though I'd prefer it not be public).

Thanks

Dave

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pasi
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Re: Hiss only after first MIDI played note on 1053

Post by pasi » Tue 2017-07-25 10:07

Are you configuring / controlling through SCI or just UART?

The analog drivers are enabled with a delay. Do you get a hiss if you wait for long enough?

If there is no hiss before a note however long you wait:
1) Do you have Reverb on? The MIDI reverb is mono and low samplerate, so conceivably could cause quantization noise. If you adjust the reverb parameters with MIDI messages (or through SCI), do you get different results?
2) EarSpeaker on by having GPIO2/3 active during reset? There are just FIRs in EarSpeaker though, so any noise-like signal should clear out quickly after generation of notes end.
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Davidelvig
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Posts: 25
Joined: Mon 2015-08-24 5:25

Re: Hiss only after first MIDI played note on 1053

Post by Davidelvig » Thu 2017-07-27 7:03

It's UART midi messages.
The hiss is after the first played note... and not before... even with a long wait.

I rechecked my eagle files using an upgraded version of Eagle. I found several ungrounded gnd pins. I expect that might cause unpredictable results.

I'm remaking the board with all gnd's connected, and I'll report back. Thanks for your help.

By the way, do you gave any example schematics for the 1103?

Dave

Davidelvig
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Posts: 25
Joined: Mon 2015-08-24 5:25

Re: Hiss only after first MIDI played note on 1053

Post by Davidelvig » Thu 2017-07-27 7:10

By the way... I think I fell into a previously-known Eagle gap.
I used ground planes on top and bottom... assuming it would pick up all open gnd pins... or report an error on rules check (drc) if any pins were unconnected

The older version (1 yr old) did not do either.

The newest version of Eagle reports Airwire errors on the same brd files, though it does not point right to them. You must dig a bit. I just happened to upgrade due to a new mac.

So...
Use the newest Eagle

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