91 HD radio technology overview for troubleshooting concerns
91 18 96 2026611/6 May 4, 2018. Supersedes Technical Service Bulletin Group 91 number 15-24 dated
November 11, 2015 for reasons listed below.
Model(s)

Year

VIN Range

Vehicle-Specific Equipment

All

2010 - 2020

All

With HD radio

Condition
REVISION HISTORY
Revision

Date

Purpose

6

-

Revised header data (Added models and model years)
Revised Condition (Added Note)
Revised Service (Updated website)

5

11/11/2015

Revised header data (Added model years)
Revised Technical Background (Added information about radio text
information)

4

07/10/2012

Revised header data (Added model year 2013)

This Technical Bulletin provides an overview of HD Radio technology and terminology. The following questions
are addressed:
 What is HD radio?
 What is HD radio “multicasting” (HD2, HD3, and etc.)?
 What is the technology behind the digital HD radio signal?
 Can HD radio be turned off?
 What is “blending”?
 What is audio level “alignment” and “misalignment”?
 What can affect HD radio reception?
 Why does the radio text information not show at times?
Note:
This TSB only applies if the vehicle has HD radio.

Page 1 of 4
© 2018 Audi of America, Inc.
All rights reserved. Information contained in this document is based on the latest information available at the time of printing and is subject to the copyright and other intellectual property rights of Audi of
America, Inc., its affiliated companies and its licensors. All rights are reserved to make changes at any time without notice. No part of this document may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, nor may these materials be modified or reposted to other sites, without the prior expressed written permission of the
publisher.

Technical Background
HD radio technology was developed by iBiquity Digital Corporation. They hold the HD radio patent and are
responsible for providing licenses to radio stations nationwide to allow the stations to broadcast with HD radio
technology.
What is HD radio?
HD radio is a digital rebroadcast of the same analog signal content coming from the source radio station and
applies to HD 1 only. HD radio signals can be found on both AM and FM bands.
 AM stations broadcasting with HD radio technology will have the same or similar sound quality as an analog
FM broadcast.
 FM stations broadcasting in HD radio technology will have the same or similar sound quality as a retailpurchased CD (burned CD sound quality can vary).
What is HD radio “multicasting” (HD2, HD3, etc.)?
Multicasting is when a radio station provides a digital
only sub-station on HD2, HD3, and etc. (Figure 1).
 There is no duplicate analog station for these
multicast stations.
 FM station providers are able to offer this
additional content because the digital conversion
of the normal analog signal opens up a larger
amount of available bandwidth.

Figure 1. Display of HD Radio station using multicasting.
What is the technology behind the digital HD radio signal?
 A digital HD radio signal is transmitted along with the analog signal, but is broadcasted at reduced signal
strength. The two signals are overlaid with each other and sent at the same time.
 A digital HD radio signal area of coverage is approximately 90% of the area of coverage for the analog signal.
The area of coverage can be affected by the environmental conditions and it is not a uniform area of coverage.
Can HD radio be turned off?
 The user can control whether or not the HD radio stations are shown in the MMI by turning the feature on or off
in the Radio Settings or in the Setup menu of the MMI.
 Refer to TSB 2026657: HD radio presets for additional information regarding the effect of stored HD radio
presets on this setting.

Page 2 of 4
© 2018 Audi of America, Inc.
All rights reserved. Information contained in this document is based on the latest information available at the time of printing and is subject to the copyright and other intellectual property rights of Audi of
America, Inc., its affiliated companies and its licensors. All rights are reserved to make changes at any time without notice. No part of this document may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, nor may these materials be modified or reposted to other sites, without the prior expressed written permission of the
publisher.

What is “blending”?
Blending is the switching back and forth of the analog and HD radio digital signals and is considered a normal
condition. Blending will occur more frequently when the vehicle is driven in and around the fringe area of
reception for the digital signal.
 Blending only takes place when the vehicle is driven in and out of the HD radio digital signal coverage area.
 Blending produces a change in sound, tone, and quality that can lead to customer concerns.
 Blending only occurs on the main HD1 station.
 Blending does not occur on the multicast sub-stations of HD2, HD3, etc. because there is no analog back-up
for this programming. Instead, the audio will be muted when outside the area of coverage.
What are audio level “alignment” and “misalignment”?
 Audio level alignment is the syncing of the digital HD radio signal and analog signal. It is designed to make the
blending process smooth.
 Misalignment is when the digital and analog signals are out of sync:
 Echoing (which sounds like a time delay between the two signals) can occur during misalignment.
 The volume level can change up or down when misalignment occurs. This happens during the switch
between analog and digital signals. The radio station broadcasting the content is responsible for the
alignment of the digital HD radio signal and analog signal audio levels.
 Concerns caused by misalignment are not a vehicle issue and replacing parts will not resolve the concern.
Report any of the above alignment conditions to the respective local radio station.
What can affect HD radio reception?
The reception of a digital HD radio can be interrupted when the vehicle is driven near high terrain, high buildings,
bridges, tunnels, and etc.
Why does the radio text information not show at times?
 The radio text information is digitally encoded in the digital broadcast. Occasionally, due to low signal strength,
the radio text information may not be available in the “Now Playing” or main radio screen.
 The radio text information is controlled by the radio broadcast station, and it is possible that the broadcaster is
not sending data or is sending invalid data.
 The radio text is automatically updated when new information is received. This may create a customer concern
of the radio text being incorrect because the radio will retain the older radio text information until new data is
received.
 HD radio text information is not updated in the “Presets” menu. However, radio text can be seen in the
“Presets” menu if the data was previously updated in the main radio menu because the data shown is the data
that was last available in the main radio menu. To update the radio text information, the customer must
navigate back to the main radio menu and allow the radio text to update before going back to the “Presets”
menu. The “Presets” menu was not designed to be the main view for operating the radio.

Page 3 of 4
© 2018 Audi of America, Inc.
All rights reserved. Information contained in this document is based on the latest information available at the time of printing and is subject to the copyright and other intellectual property rights of Audi of
America, Inc., its affiliated companies and its licensors. All rights are reserved to make changes at any time without notice. No part of this document may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, nor may these materials be modified or reposted to other sites, without the prior expressed written permission of the
publisher.

Production Solution
Not applicable.

Service
 See the attached troubleshooting guide to aid in diagnosis.
 Contact the Technical Assistance Center if the troubleshooting guide does not help resolve issues with HD
radio.
 To learn more about HD radio, visit http://www.hdradio.com/.
 Report station issues at: https://hdradio.com/stations/feedback.

Warranty
This TSB is informational only and not applicable to any Audi Warranty.

Additional Information
The following Technical Service Bulletin(s) may be necessary to complete this procedure:
 TSB 2026657, HD radio presets.
All parts and service references provided in this TSB (2026657) are subject to change and/or removal. Always
check with your Parts Department and/or ETKA for the latest information and parts bulletins. Please check the
Repair Manual for fasteners, bolts, nuts, and screws that require replacement during the repair.
©2018 Audi of America, Inc. All rights reserved. Information contained in this document is based on the latest
information available at the time of printing and is subject to the copyright and other intellectual property rights of
Audi of America, Inc., its affiliated companies and its licensors. All rights are reserved to make changes at any
time without notice. No part of this document may be reproduced, stored in a retrieval system, or transmitted in
any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, nor may these
materials be modified or reposted to other sites without the prior expressed written permission of the publisher.

Page 4 of 4
© 2018 Audi of America, Inc.
All rights reserved. Information contained in this document is based on the latest information available at the time of printing and is subject to the copyright and other intellectual property rights of Audi of
America, Inc., its affiliated companies and its licensors. All rights are reserved to make changes at any time without notice. No part of this document may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, nor may these materials be modified or reposted to other sites, without the prior expressed written permission of the
publisher.