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PRODUCT MANUAL
3.2
Bluetooth Audio Transmitter Operation
The Bluetooth Audio Transmitter is configured to implement an A2DP profile in source mode. In this
mode, the transmitter encodes audio, and sends it over the Bluetooth link.
1. Upon power up the LED will be off. The unit will search for an attempt to pair with the last paired
headphone. If a headphone is found then it is connected and the LED will turn on.
2. If the button is pressed, then any stored pair is deleted and the unit goes into AutoPair mode for
60 seconds. The blue light blinks while in AutoPair mode. The Bluetooth Audio Transmitter will
pair with the first headphones it finds that are also in pairing mode. If no connection is found the
LED will turn off and the unit will go into standby and make no connection until the button is
pressed again.
3. If a paired headphone is removed or powered off, the blue LED status light will turn off. The unit
will wait for the return of the headphone and automatically re-pair when found.
3.2.1 BT Transmitter: LED Status Quick Summary
Fast blink of blue status LED (frequency 2 blinks / sec) - In AutoPair mode. Will connect to first
headphones it finds that are also in pairing mode.
Solid blue status LED- BT transmitter is currently paired with a device.
No blue status LED- BT transmitter is not paired. If there is a previous pairing then the unit will attempt
to connect with the last paired headphones.
3.2.2 BT Transmitter: Operation Quick Summary
Button press - BT Interface disconnects from currently paired device and places the unit in AutoPair
mode for 60 seconds. To connect to a headphone you must place the headphone in pairing mode.
3.3
Notes on Latency
The Bluetooth Audio stream introduces latency (delay) in the audio signal. Typically this latency is
approximately 150 ms. This small delay is unimportant unless the audio is accompanying a video
image. In this case any delay greater than about 50mS can be detected as lack of synchronization with
lips or other sounds on the video. Typically a modern device such as a smart phone or tablet will adjust
the video to insure synchronization when it knows that the audio is going over a Bluetooth stream.
Therefore, the Alto BT Receiver should always provide synchronized audio if the user connects a
modern device to watch video.
The BT Transmitter however cannot adjust the video delay on the cabin monitor because they are
independent and unrelated subsystems, unlike the video / Bluetooth audio relation in an integrated
device such as a tablet or cell phone. In this case it is important to employ Low-Latency headphones if
the user desires to view cabin video while listening to the audio over the Bluetooth link. The Alto BT
Transmitter incorporated a special codec known as aptX-LL®. A list of headphones supporting the
aptX-Low Latency can be found here
https://www.aptx.com/products?field_aptx_type_tid=484&field_product_category_tid=125
A V I A T I O N
Size
Doc Type
Drawing Number
A
PM
107840-XXXX-XXXXXPM
107840 Bluetooth Audio Interface
Rev
Date
3
04/11/19
Page
16
of
25
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