Gentner AP800 noise cancellation for VR


Active Member
I posted some MP3 recordings on the HS board that demonstate the noise cancelling setup I've installed for using voice recognition with HomeSeer.

A brief summary: Crown MB3 mics installed into the walls of 8 rooms connected back to a Gentner AP800 audio conferencing mic mixer. This mixer provides phantom power to the mics and also provides Digital Signal Processing (DSP). DSP allows you to electronically "cancel" sounds so that the mics don't pick them up.

I have the outputs from my TV, and whole-house audio connected for cancellation. This allows you to issue VR commands with great success while the tv is on or music is playing and also cancels the TTS announcments so HomeSeer doesn't hear itself.

The Genter AP800 also has digital outputs that represent which mic is gated on. Theses are connected to an SECU-16 on my HomeSeer server so it knows which room I'm speaking from. This simplifies VR command so you can just say "lights on" instead of "Living Room Lights On".

Have a look here if interested:
Post on HomeSeer Message Board

I thought so, but right now $150 on eBay with 18 hours remaining. I'm watching it assuming it will be a bit higher than normal based on the "Home Automation" effect!
I have been watching eBay for a while, they always end up going for much more than what I could afford, but at least now I know how to correctly implement VR :)

Paul: Are you getting any false commands triggered by noise? How about reliability, do you ever have to repeat yourself?
If memory serves me well, the Gentner products were originally designed for phone call mixing. Setting up a "Mix Minus" meaning the output contains all singal with the exception of the input. Most radio shows use a system like this. The Gentner units are special because they add in a gate and have auto cancellation of stray noises which reduces even further the chances for mis-fires and hum, echo or feedback.
What is gate? I've seen this mentioned time and time again but I have no idea what it means in the microphone/sound world.

I'll write up a better description of the AP800 when I have a few more minutes and will include info on gating.

Quick answer until Pk can get more in depth, a gate essentially acts as an automatic volume control when the level of audio drops below a set value.

For example, on a podium microphone, someone speaking in a normal tone speaks at 60db, if the input level drops below 40db, no audio is amplified from that microphone. This reduces background noise and in most cases feedback and ground noise.

Staying with out podium, as you paused in a speech, the gate would ignore all audio under 40db from the table guests on the dais who are murmering away.
electron said:
Paul: Are you getting any false commands triggered by noise? How about reliability, do you ever have to repeat yourself?

I normally keep VR "waiting for attention", so stray sounds don't cause false triggers. My attention phrase is "attention automation computer"... it's fairly long, but seems natural and is complex enough that I only have 1-2 false "attentions" per year.

After issueing my attention phrase I figure I get about 90% accuracy with VR commands, this means that maybe 1 out of 10 times I'll have to repeat a command to get it to work.

In my opinion it's very useable. I do issue the "ignore" phrase when I'm done using VR to put it back to "waiting for attention" to eliminate false triggers.

Me: Attention automation computer
TTS: yes, Paul
Me: What's the weather like?
TTS: The weather is blah, blah blah...
Me: Lock the doors
TTS: Locking the doors now
Me: Thank you
TTS: Call when you need me

If I leave HomeSeer "listening for commands", the house will trigger all sorts of events and quickly go crazy. This hasn't been a problem for me as long as I issue the ignore phrase when done with VR. HS is also set to automatically switch to "waiting for attention" after 60 secs in case I forget.

pkoslow said:

I'll write up a better description of the AP800 when I have a few more minutes and will include info on gating.

Here's a copy of what I posted on the HS board. It describes some of the AP800 features that are useful for VR. I pulled this all right from my head, so hopefully the naming is similar to what the AP800 manual uses:

The AP800's are very capable with LOTS of features. I'll take a shot at describing some of the basics and also explaining how some of the more advanced features work:

Mixer - A mixer is a device that connects input device (mics, intruments, etc) to outputs (amps/speakers, recording devices, etc.). They also provides control over volume, tone, and routing (what input gets to what output).

If you've ever been to a live music performance you've probably seen the sound engineer sitting in front of a panel with lots of sliders & knobs. That's the mixer and the sound engineers job is to tweak the sound by adjusting the volume and tone of different performers and instruments so that what comes out of the speakers for the audience to hear sounds "good". That sound engineer may even turn off mics that aren't in constant use so they aren't picking up "noise" or contributing to feedback (remember this example when we get to "gating".

Gentner AP800 - The Gentner AP800 is an automatic mixer that was designed for audio conferencing use. It uses Digital Signal Processing (DSP) to handle lots of different functions automatically. Like the Sound Engineer, DSP is constantly listening and making adjustments to try and improve the sound. I feel it's an ideal device for Voice Recognition (VR) and it works far better that any of the previous devices that I have tried.

Gating - Gating is defined as turning a mic on when it reaches a defined threashold (sound level) and then off again when the sound lowers. Once adjusted, the mic should gate on when you speak, then turn back off when you're not speaking. As an example, the AP800 was designed to be used for audio conferencing in a conference room with mics installed around the table. If all the mics were always on, they would pick up the sound of papers shuffling, people tapping pens on the table, etc. The result would be lots of noise at the other end of the phone call. Gating allows the mic to turn on as individuals are speaking, while blocking out the sounds that would have been picked up by other mics.

The AP800 adds several other features based on gating which are very useful for VR:

Number of mics allowed to gate on at any given time. For VR use, I set this to 1. For audio conferenceing this may have been set to 2-3 which would allow more than one person to speak and be heard at the same time. For VR use, it's important to keep this set to only gate a single mic on at a time if you plan to use the mixer to tell HS what room you are speaking from
Chairman mic - This allows you to configure one or more mics to take precidence over others. In the audio conference example, you'd want the leader(s) mic(s) set to chairman so if during the call an argument breaks out the leader(s) can always speak up and their mic will gate on so they can be heard.

In a VR setup this is helpful too. I have my Office, Living Room & Kitchen mics set to "chairman mode". If my girlfriend is using the hair dryer in the master bath, the noise will gate on the bathroom mic. I can still issue VR commands from the three rooms that are set to "chairman mode" while she's drying her hair because those mics will still gate on while gating off the bathroom mic to block the hair dryer noise from interfeering.

Adaptive Ambiance - With adaptive ambiance enabled, DSP is always monitoring the sound level in the house. If noise levels increase from something like a washing machine or dishwaser running, the threashold requird to gate the mic on is increased proportionaly.

Digital Outputs - The AP800 has digital outs that represent the mic gating status. These outputs effectively close a contact when a mic is gated on and open the contact when the mic is gated off. I've got these outputs connected to a SECUi-16 and with a little bit of scripting, HS knows which room I'm speaking from (which mic is gated on). This is why it's important that only 1 mic is allowed to gate on at any given time.

With this setup, you can simplify VR commands so that it's only required to say "lights on" instead of "living room lights on".

Echo Cancellation (noise reduction) - In it's audio conferencing role, this feature of the AP800 is used to minimize audio feedback and "echo" which everyone has experienced when using a speaker phone (sounds like you're in a cave). For VR use, this feature opens up even greater possibilities! If you connect the outputs of your home audio devices like the TV, Stereo and TTS to inputs on the AP800, it can effectively cancel the audio as demonstated in my recordings. DSP does this by comparing the signal that is receved from your stereo and comparing it to what the microphone is picking up. It determines what's "different" and strips out the rest leaving a signal with the stereo sound removed or greatly suppressed.

This helps VR hear your voice over the TV or music that's playing, but equally as important, it keeps the TV, stereo, or TTS from gating on a microphone. This is useful for me, because my TTS announcements play throughout the house on speakers built into the walls. Without this echo cancellation capability TTS announcement would gate random mics on around the house as HS speaks. This causes trouble if you are trying to use the gate status to tell HS where you are speaking from.

Some lesser mixers proving gating status, but without the echo cancellation this doesn't work well.

Example: I'm in the Kitchen and issue the VR command "What's the tempurature". TTS will announce "The tempurature outside it 65 degrees" throughout the house. Without the echo cancellation capability, the TTS announcement itself will likely gate on a mic in another room, maybe the bedroom. Now HS thinks I'm in the bedroom instead of the Kitchen. This doesn't alwasy cause problems, but if you start doing complex interactions with HS using VR commands dependant on knowing your location via mic gate status, it starts to fall apart quickly. With the echo cancellation, this isn't an issue as the mics "can't hear" the TTS announcements.

Inputs & Outputs - The AP800 has 12 inputs and 12 outputs that can be configured using the matrix mixer which basically means that any or all inputs can be routed to any or all outputs in any combination... very powerful for routing audio signals!

Each input has a 3-band EQ that can be used to adjust the audio tone as well as high & low pass filters which allow the mixer to filter out certain noise. This works good to eliminate the rumble from HVAC or other types of noises that are constant in tone.

Control - The AP800 has an RS-232 port that allows you to control all features and functions from your PC. It even has 8 presets that can be configured and then recalled by HS using scripts.

Wow... that's a lot of typing and really just scratches the surface on the AP800 capabilities. I've covered some of the important features that are useful for VR, but the device is capable of lots more.

I'd recommend downloading the manual that is available from for anyone that is interested in learning more about this device.

Happy Holidays,