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| [ Also see: Bluetooth
Headsets and Hands-Free Bluetooth
Mobile Phones ]
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Recent Audio Headlines
All About Symbian Video titbits from SEE 2009
To give you a taster of SEE 2009, here's a little video selection (embedded below), with three interviews I did at the event: with Tieto (Qt developers, in this case), TAT (demo of '3D' interface) and Stantum (demoing their resistive multitouch testbed). Watch out for Rafe's video tour of the whole event and for various (longer) audio podcasts in the coming week.
FreshPatents.com Citizens band radio with wireless cellular telephone connectivity
A wireless communication device for use in connection with a cellular telephone is disclosed and a transceiver radio such as a citizens band radio. The wireless communication device of the present invention provides enhanced audio broadcasting capabilities for an operator of the device by providing a larger, more powerful speaker...
BBC Audio slideshow
British Library's look at 19th century photography
FreshPatents.com Method and apparatus for estimating high-band energy in a bandwidth extension system
A method (100) includes receiving (101) an input digital audio signal comprising a narrow-band signal. The input digital audio signal is processed (102) to generate a processed digital audio signal. An estimate of the high-band energy level corresponding to the input digital audio signal is determined (103). Modification of the...
FreshPatents.com Method and device for checking a subscriber line
In a method for checking a subscriber line with a first and a second electrical line, wherein each line is connected to an encoder/decoder via a subscriber line circuit, the first line is connected to ground, a resistance of the second line is increased, an audio signal is outputted from...
GPRS News Keep an eye on your home,
a URL with log-in and password. The visuals are then beamed to the user's mobile over a GPRS connection. If something unusual happens, the system can even send an SMS alert. However, there is no audio support at present. The visuals are very fast, clear
Bluetooth News Plantronics voyager pro uc headset... (Ubergizmo via TechNews AM)
and their latest release, the Voyager PRO UC headset is no different by merging the award-winning Voyager PRO Bluetooth headset with a plug-and-play Bluetooth USB adapter, enabling richer wideband audio on softphones alongside Voyager PRO’s superior
Bluetooth News Faceid system for easy recognition... (Ubergizmo via TechNews AM)
and their latest release, the Voyager PRO UC headset is no different by merging the award-winning Voyager PRO Bluetooth headset with a plug-and-play Bluetooth USB adapter, enabling richer wideband audio on softphones alongside Voyager PRO’s superior
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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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