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| [ Also see: Bluetooth
Headsets and Hands-Free Bluetooth
Mobile Phones ]
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Recent Audio Headlines
FreshPatents.com Managing the audio-signal loss plan of a telecommunications network
A method is disclosed that enables the monitoring, evaluation, and adjustment of a telecommunications network's audio-signal loss plan. The method can be implemented at a data-collection server, in which the server accumulates voice-quality measurement statistics from various nodes in the network. Such nodes include telecommunications endpoints, media gateways, private-branch exchanges,...
FreshPatents.com Digital broadcast transmitting apparatus, digital broadcast receiving apparatus, and digital broadcast transmitting/receiving system
A transmitting apparatus includes: a data packet generating unit which generates a data packet including encoding information that is not included in the header information of an audio stream packet and that indicates whether any processing is included which causes the decoding time of the encoded audio signal to exceed...
FreshPatents.com Directional warning systems
When vehicles are operating in reverse and backing up, there are significant dangers to pedestrians. Vehicles in which directional warning systems can be used on comprise large trucks and trailers, small vehicles, and construction and agricultural equipment and others. Directional warning systems is designed to warn pedestrians via audio and...
GPS News Mio Moov 200 SatGuide GPS Navigation System
No audio out GPS UI could have been better arranged GPS is increasingly becoming quite popular amongst our active motorists. We may know the city we live in like the back of our hand
BWE Magazine Avis Will Have Florida Travelers Beaming With Broadband Wireless Satellite TV and Audio Service with New In-Car TV Service
Avis Rent A Car and RaySat Broadcasting (RBC) announced that Avis renters at select locations can now enjoy the ride with AT&T CruiseCast service, a new satellite TV technology that delivers 22 video satellite channels as well as 20 audio channels to a mobile unit in automobiles. Beginning today, Avis renters at airport locations in Ft. Lauderdale, Miami, Orlando, Tampa and West Palm Beach can rent AT&T CruiseCast for $8.95 per day or $62.65 per week.
FreeNewsFeed More Courthouses Switching To Digital Technology
Courts in Iowa, Minnesota and New York are considering replacing at least some court reporters with digital recording systems to cut costs.
If they do, they would follow Utah, Vermont, New Hampshire, Alaska and Kentucky in using electronic recording systems. Utah and Vermont switched exclusively for budget reasons in 2009, according to SueLynn Morgan, president of the National Court Reporters Association (NCRA), and officials in those states.
"The budget crisis since January 2009 is behind the push now,"...
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Bluetooth Audio Resources
 Useful
technical resources for Bluetooth audio.
In this
section:
On the Bluetooth air-interface, either a 64 kb/s log PCM format
(A-law or μ-law) is used, or a 64 kb/s CVSD (Continuous Variable
Slope Delta Modulation) is used. The latter format applies an adaptive
delta modulation algorithm with syllabic companding.
The voice coding on the line interface should have a quality equal
to or better than the quality of 64 kb/s log PCM.
LOG PCM CODEC
Since the voice channels on the air-interface can support a 64 kb/s
information stream, a 64 kb/s log PCM traffic can be used for
transmission. Either A-law or μ-law compression can be applied.
In the event that the line interface uses A-law and the air interface
uses μ-law or vice versa, a conversion from A-law to μ-law
is performed. The compression method follows ITU-T recommendations G.
711.
CVSD CODEC
A more robust format for voice over the air interface is a delta
modulation. This modulation scheme follows the waveform where the
output bits indicate whether the prediction value is smaller or larger
then the input waveform. To reduce slope overload effects, syllabic
companding is applied: the step size is adapted according to the
average signal slope. The input to the CVSD encoder is 64 ksamples/s
linear PCM. The system is clocked at 64 kHz.
Voice Codecs
| Linear |
CVSD |
| 8-bit logarithmic |
A-law
μ-law |
Voice coding schemes supported on the air interface.
The appropriate voice coding scheme is selected after negotiations
between the Link Managers.
Block diagram of CVSD encoder with syllabic
companding.
Block diagram of CVSD decoder with syllabic
companding.
Accumulator procedure.
Error Handling
In the DV and HV3 packet, the voice is not protected by FEC. The
quality of the voice in an error-prone environment then depends on the
robustness of the voice coding scheme. CVSD, in particular, is rather
insensitive to random bit errors, which are experienced as white
background noise. However, when a packet is rejected because either
the channel access code or the HEC test was unsuccessful, measures
have to be taken to “fill” in the lost speech segment.
The voice payload in the HV2 packet is protected by a 2/3 rate FEC.
For errors that are detected but cannot be corrected, the receiver
should try to minimize the audible effects. For instance, from the
15-bit FEC segment with uncor-rected errors, the 10-bit information
part as found before the FEC decoder should be used. The HV1 packet is
protected by a 3 bit repetition FEC. For this code, the decoding
scheme will always assume zero or one-bit errors. Thus, there exist no
detectable but uncorrectable error events for HV1 packets.
General Audio Requirements
Signal levels
For A-law and µ-law log-PCM encoded signals the requirements on
signal levels follows ITU-T G.711.
Full swing at the 16 bit linear PCM interface to the CVSD encoder
is defined to be 3 dBm0. A digital CVSD encoded test signal is
provided in a Test Signal file available on the website. This signal
is generated by a software implementation of a reference CVSD encoder.
The digital encoder input signal (1020 Hz, sine-wave) generating the
test signal has a nominal power of -15 dBm0. When the CVSD encoded
test signal is fed through the CVSD receiver chain, the nominal output
power should be -15 ± 1.0 dBm0.
CVSD audio quality
For Bluetooth audio quality the requirements are put on the
transmitter side. The 64 ksamples/s linear PCM input signal must have
negligible spectral power density above 4 kHz. A set of reference
input signals are encoded by the transmitter and sent through a
reference decoder (available on the website). The power spectral
density in the 4-32 kHz band of the decoded signal at the 64 ksample/s
linear PCM output, should be more than 20 dB below the maxi-mum in the
0-4 kHz range.
For more details see the Bluetooth Specification section 12 -
Bluetooth Audio.
- Headset Profile The
Headset profile defines the requirements for Bluetooth devices
necessary to support the Headset use case.
- Fax Profile The Fax
profile defines the requirements for Bluetooth devices necessary to
support the Fax use case.
- Cordless Telephony
Profile This profile defines the features and procedures that
are required for interoperability between different units active in
the ‘3-in-1 phone’ use case.
- Intercom Profile
This profile defines the requirements for Bluetooth devices
necessary for the support of the intercom functionality within the
3-in-1 phone use case.
- Dial-Up Networking
Profile The Dial-up Networking profile defines the requirements
for Bluetooth devices necessary to support the Dial-up networking
use case.
- Wireless Headset
Audio Quality The maximum throughput of BT on the forward path
is 723.2 Kbps (DH5 mode). CD-quality audio is 44100 * 16 bits/sample
* 2 channels (stereo) -> 1411.2 Kbps. Thus on its own BT headset
would only be able to handle mono CD-quality audio. However...
- Variable/Fixed
CVSD Encoder/Decoder Values? The CVSD encoder/decoder parameters
(such as h & Beta) are not variable, as some people might
believe, but fixed...
- Changing CVSD
Encoder/Decoder Values The CVSD values given in the Spec (also
see Variable/Fixed CVSD Encoder/Decoder Values? ), are designed for
a 16-bit encoder/decoder. However will they change for a 13-bit
design?
- Service Records for
Headset Audio Gateway In the Service Record for Audio Gateway
,UUIDs of Headset (0x1108) are used. However UUIDs for
HeadsetAudioGateway (0x1112) exist, but are not used...
- Ericsson
Development Kit, CVSD/PCM Voice Coding? Ericsson's development
tool is using linear PCM for voice coding. But in its BT module
specs, it recommends CVSD...
- CVSD Encoder Input
Issues Section 12.2 of Bluetooth Specification version 1.0 B
states; "The input to the CVSD encoder is 64k samples/s linear
PCM." However could you create the 64 kbit/s encoder output
using just using a 8k samples/s input?
- Bluetooth Headsets and Handsfree
Resources and products search.
- Bluetooth USB Adapters Resources and
products search.
- Bluetooth Mobile Phones Resources and
products search.
- Voice Encoding Methods for Digital
Wireless Communications Systems - Bryan Douglas (PDF, 128Kb)
Wireless communications operators see phenomenal growth in consumer
demand for high quality and low cost services. Since the physical
spectrum for wireless services is limited, operators and equipment
suppliers continually find ways to optimise bandwidth efficiency.
Digital communications technology provides an efficiency advantage
over analog wireless communications; multiplexing and filtering is
easier, components are cheaper, encryption is more secure and
network management is easier. Additionally, digital technology
provides more value added services to customers...
- Application of Bluetooth Wireless
Technology to Guided Audio Tours - University of British Columbia
(2001, Zipped PDF, 1.8Mb) This work demonstrates key
applications and strategies that many believe will be crucial to
Bluetooth’s success: * voice-based services and information
access, * multimode operation with flexible delivery options, *
proximity-based applications with automatic connection to public
access points, * applications with revenue generating potential...
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