Reducing the beeps from the JBL amp

[brosnan]

Sorry to start another thread on beeps, but let's focus this one on how (or if) we can reduce the volume (to zero?) of the loud beeps which occur when pressing MFD or steering wheel beeps. These were recently discovered by SynergyGuy to be generated inside the JBL amplifier under the passenger seat (for those with the external amp option).

I've found the beeps are added to all speaker outputs inside the JBL unit. Seat belt related beeps come from somewhere else - no the audio speakers.

At http://www.wb5mrn.com/prius/jblpcb.jpg is a photo which describes the structure of what's inside. It seems the MFD generates an AVCLAN command (see http://www.wb5mrn.com/prius/beep_command.jpg ) which is a request for beep. This is detected by the NEC uPD6708 IEBus controller which notifies the Analog Devices DSP microcomputer. The DSP chip synthesizes a sine wave and adds it (along with any equalization and other signal processing it might be doing on the main audio) to all the I2S serial digital audio outputs going to the Asahi Kasei DACs. Those chips generate the waveforms which are amplified and sent to the speakers.

I was kind of hoping there was a analog tone generating chip. That way we could have reduced the beep amplitude with a volume knob. But it's deeping integrated into the firmware running on the DSP chips (presumably stored in the 2M Flash memory). So the options seem to be

A) Decipher the instructions in the Flash memory and find the part that does beeping and rewrite it for a different amplitude or frequency that's less annoying and re-flash the contents.

or

Detect the beep command with a small microcontroller monitoring the serial data between the uPD6708 and the DSP chip, then activate the mute line for about 50ms to supress the beep sound.

These are both hard. I feel there's a chance I might be able to do item B, but I'm hoping someone can come up with a simplifying idea. Any thoughts?

[knowledgeseeker]

<div class='quotetop'>QUOTE(brosnan\";p=\"77985)</div>

... I'm hoping someone can come up with a simplifying idea.  Any thoughts?[/b]

Some thoughts ...

Presumably the coding could be changed at either end - at the MFD where the beep signal is sent, or at the JBL where it is decoded. Perhaps one is simpler than another

In the other "beep" thread it was noted that the Land Cruiser uses a similar setup, but with an analog amp. That amp might not know how to decipher the beep codes - and it might produce better sound. If it is possible to learn more about the LC amp, that might be a route. If someone has a chance to take a test drive or look through the LC manual, the beep behavior might be checked.

Good luck - fixing this would repair the single most annoying "feature" of the car (for me - probably the bladder is a big issue for many).

[brosnan]

Good point about dealing with the beep on either end. That triggerred another thought. Maybe it's possible to build a little box that's in series with the 2 AVC-LAN wires. On the MFD it would pretend to be the JBL amp and listen to commands coming from the MFD. After decoding them, it would pass the commands on if they were volume, fader, tone adjust or similar commands. Beep commands would not be passed on. In fact they could trigger some circuit of our own choosing to make clicks or beeps which are adjustable and less annoying.

[Sufferin' Prius Envy]

Maybe you could introduce a virus which would kill the beep, or at least change it into a quiet sneeze. :wink:

[brosnan]

The data sheet for the 6708 ( http://www.necel.com/nesdis/image/U10680EJ2V0DS00.pdf ) gives all the detail of the AVC-LAN (IEBUS) signalling. From that the beep command waveform can be decoded. Each low going pulse is a 0 if narrow and a 1 if wide. The upward isolated blips are the boundaries between master (MFD) and slave (JBL) talking. So here's the detail of the beep message:

Header = 0x3 (start bit + not a broadcast)
Master Address = 0x110 (The MFD's address I guess)
Slave Address = 0x440 (The JBL's address I guess)
[ACK] (first upward blip)

Control Field = 0xf (write data)
[ACK]

Message Length Field = 0x5 (5 bytes of data will follow)
[ACK]

Data Field = 0x00
[ACK]

Data Field = 0x5E
[ACK]

Data Field = 0x29
[ACK]

Data Field = 0x60
[ACK]

Data Field = 0x01
[ACK]


So in hexadecimal, the beep command is the 5 byte sequence 00 5E 29 60 01

Next - how to best detect or surpress these. One possibility: Use a microcontroller to detect this pattern, but before it gets to the end, mess up the last data byte so the parity bit will be wrong and the JBL won't (I hope) make the beep noise. Another possibility is that those 5 bytes include a volume parameter for the beep (and maybe frequency).

[bobc]

Caveat: I have no clue what I'm tallking about...

But, is it possible to just build a filter that filters out that freq. of the beep?

[V8Cobrakid]

i was going to post something like this.. but found i am also lost on what i'm talking about. I think you might have to add a "simple" filter like this to every speaker like. I think it would also kill the voice command been.

quite a task on your guys hands. Hope you figure something out. You will help save us all from the evil beeps.

[brosnan]

I did think about a filter to get rid of the tone used in the beeps. Two things about this make it hard - one is to not affect sound quality (who knows - some music might contain exactly that same note) and the other is that there are at least 6 separate places where the filter is needed. Unfortunately those 6 channels are not all derived from one place - that could have limited it to a single filter.

Keep the ideas coming, though!

[naterprius]

Mike, a much easier approach; just change the destination address to be something other than the JBL Amp! Perhaps the Amp would ignore the message on the bus?

Nate

[engunneer]

As an EE, I'd actually engoy making a circuit to eat the beep command, but, it doesn't annoy me much, and I don't want to go tearing into my dashboard anytime soon, as I've only had the car for a fortnight. Anyone in the Seattle area willing to test a circuit if I build it?