ANALYSIS OF AUDIO RECORDINGS MADE USING THE VOICE RECORDER APPLICATION ON

ANDROID PHONES

by

GINA ANTOINETTE DEANGELIS

A.A., Arapahoe Community College, 1999

B.S., University of Colorado Denver, 2001

A thesis submitted to the

Faculty of the Graduate School of the

University of Colorado in partial fulfillment

of the requirements for the degree of

GINA ANTOINETTE DEANGELIS

This thesis for the Master of Science degree by

Gina Antoinette DeAngelis

has been approved for the

Catalin Grigoras, Chair

Jeff M. Smith

Marcus Rogers

Date: May 16, 2020

DeAngelis, Gina Antoinette (M.S., Recording Arts)

Analysis of Audio Recordings Made Using the Voice Recorder Application on Android

Phones

Thesis directed by Associate Professor Catalin Grigoras

ABSTRACT

Android is one of the two main operating systems for mobile phones and includes

an application for voice recording. Since extensive research has been completed on the

"Voice Memos" application for iOS, there remains research to be completed on the default

application for the Android OS. This thesis explores the user interface for four different

Android phones with four different voice recording application versions. Features,

limitations, editing capabilities, file formats and atom structure for each phone are

discussed. A testing protocol was created and utilized for the creation of the test

Your sacrifices did not go unnoticed.

ACKNOWLEDGEMENTS

First, I would like to thank Rich Sanders who first introduced me to audio forensics.

His passion for audio and his brilliance were inspiring and I wish I hadn’t waited 16 years

to finally see this through. You are truly missed!

Secondly, to my mom who helped proofread and edit all my papers from elementary

school all the way through this thesis. Your dedication and support have been incalculable.

I could not have done this without you!

To Andrew Hill whose thesis, “Analysis of Audio Recordings made using “Voice

To my 17-19 cohort, thank you for all your support, encouragement and “late night

seminars”. I feel very honored and privileged to be a part of such a great group! A special

shout out to Doug – thank you for the hours spent with me over the phone, over the

computer and via email “holding my hand”. You mentored me and helped me laugh

through the most stressful times of the program. I hope to repay the favor someday.

To my Heavenly Father who made everything possible, thank you!

CHAPTER

Android Devices................................................................................................................................. 3

Previous Research ............................................................................................................................ 3

II. VOICE RECORDER USER INTERFACE ............................................................................................. 5

Device #1: HTC One, Android 5.0.2 Lollipop, Voice Recorder 6.3.843363 ................. 5

Editing ........................................................................................................................................... 10

Editing ........................................................................................................................................... 21

Interrupted Recordings with Phone Calls....................................................................... 23

LG Q6 ................................................................................................................................................... 24

Samsung S6 and S9 ........................................................................................................................ 25

Device #1: HTC One ...................................................................................................................... 27

Device #2: LG Q6 ............................................................................................................................ 30

Consistencies and Inconsistencies..................................................................................... 30

viii

Atom Structure .......................................................................................................................... 31

Device #3: Samsung S6 ................................................................................................................ 31

Consistencies and Inconsistencies..................................................................................... 31

Atom Structure .......................................................................................................................... 32

Device #4: Samsung S9 ................................................................................................................ 34

Consistencies and Inconsistencies..................................................................................... 34

Atom Structure .......................................................................................................................... 34

V. CONCLUSION ......................................................................................................................................... 36

TABLE

1: Mobile Phone Overview ................................................................................................................................. 2

2: Digital Audio Specifications ......................................................................................................................... 5

3: Comparison of Unedited and Edited Recordings on the Q6 ......................................................... 31

4: Comparison of Unedited and Edited Recordings on the S6 .......................................................... 33

5: Comparison of Unedited and Edited Recordings on the S9 .......................................................... 35

CHAPTER II

All phones investigated had unique audio encoding and container properties. Audio

encoding algorithms determine how the file will be encoded (written) and decoded (played

back). The container (wrapper) specifies how the media data and metadata is organized

[5]. The table below gives an overview of all phones and their file formats. It also includes

their bit rate and sample rate. Each one is discussed in detail with each phone that was

tested.

m4a

Features and File Formats

This version of the Voice Recorder app has several different options and settings for

the audio recordings. It contains the basic controls of “record”, “pause”, “stop”, and “play”.

Once a recording is made, the user is prompted to keep the default name or to rename it

(Figure 4). There is also an option to rename the file later if needed. The audio file can be

shared through several communication applications including but not limited to: messages,

drive, email, Gmail and others depending on what is installed on the phone. The files can

also be deleted and removed from the app. (It is unknown whether the phone retains the

Figure 3: Voice Recorder While Recording

The Voice Recorder app on the HTC One records only in mono from the built-in

microphone, but allows for three different file formats: normal quality which is Adaptive

Multi-Rate Narrowband (AMR-NB), better quality which is Adaptive Multi-Rate Wideband

(AMR-WB) (this is the device’s default setting) and high quality which is Advanced Audio

Coding Low Complexity (AAC-LC) (Figure 6). All of the above formats are lossy

compression formats, which means the quality of the recording is diminished and data is

lost (that cannot be retrieved in its original form) in order to save on the file size. This

phones. Since the HTC One does not have any external memory options, file size can

become a factor if the user is planning on storing a large amount of information on this

device.

AMR-NB and AMR-WB are common audio compression formats in mobile phones.

ACC-LC is another very common file format that compresses the file size. While these file

formats will not sound any different to the average listener, in a good quality listening

environment they can lose depth and richness since the quality of the audio has been

affected to save on file space.

Editing

The Voice Recorder does not have any editing capabilities. There are no options to

trim or delete any section of the recording. The user also cannot record over a previous

recording in part or in whole. However, a voice recording can be downloaded to the

computer, edited in a third-party editing software, and then downloaded again to the app

as long as the edited file is saved as any of the available file formats.

Device #2: LG Q6, Android 7.1.1 Nougat, Audio Recorder 6.1.8

and can also be saved in the app QuickMemo+ (which comes standard on the phone). Like

the HTC One, recordings can be deleted, and they will no longer be available in the app.

The Q6 phone can only record in mono and has one file format: AAC-LC at 96

kilobytes per second (kbps) 44.1kHz sample rate. This phone does offer the capacity for

external storage and the app grants the user a choice of internal or external memory before

starting the recording; however, once the recording is made, it cannot be moved to the

other storage unit.

Figure 9: Audio Recorder While Recording

It is interesting to note that the default save name includes the date of the recording

as the beginning numbers but ends with “Normal” (Figure 10). This would leave the user

to believe that there are other recording settings besides the default setting, but after

further investigation there are no other quality settings.

The details page (Figure 12) shows the user the title of the recording, the size of the

file, the date and time of the recording, the type of file, the duration, and the path where the

file is saved.

Editing

The LG Q6 does have editing capabilities. Once the recording has been completed

and saved the user can select the scissors icon (Figure 13) to edit the selected recording.

The user can share the file or delete the file here as well.

Editing

The editing capabilities of the Voice Recorder for the S6 and the S9 offer the most

options of all the recording apps tested. These phones offer the option to delete the

beginning, the middle and the end of the recording. Once the recording is saved, the user

can select “Edit” and then editing markers can be placed wherever needed (Figure 21).

Figure 22: Editing Options

If the middle of a recording is deleted, then the beginning and ending are spliced

together. If the middle of the recording is selected, then the beginning and ending are

deleted; however, a section cannot be cut and pasted in the recording or into another

recording. When editing is completed, the file can either be saved as a new file or an

overwrite of the original recording.

Any section of the recording including the whole recording can be recorded over

and it can either be saved as a new recording or an overwrite of the original recording.

app. (It is unknown whether the phone retains the audio recording or not, that was outside

the scope of this paper.)

Interrupted Recordings with Phone Calls

Since the S9 had service at the time of testing, recordings were made with an

interruption of an incoming call from another mobile phone. The first recording received a

phone call, but the call was ignored. The Voice Recording did not pause or stop if the phone

call was ignored; however, a vibrating noise is recorded in the audio.

Another recording was made with an interrupting phone call and this time the call

CHAPTER III

TEST RECORDING PROTOCOL

A testing protocol, developed by Jeff Smith, et al. for the iOS in “Triage Approach for

the Forensic Analysis of Apple iOS Audio Files Recorded Using the ‘Voice Memos’ App” [4]

was later expanded by Hill for his thesis, “Analysis of Audio Recordings made using ‘Voice

Memos’ application for iOS” [5]. Hill’s thesis protocol offered a skeleton of protocols to

start with; but since the Android OS and the iOS are very different in form and function, a

proper protocol had to be created for the Android OS. Since the HTC One had such limited

explored; therefore, a testing protocol was established. It was important to see what

artifacts were introduced into the recording by Android when the user accesses all

available options for recording and editing.

In view of the fact that there was only one quality setting for the audio, different

recordings were completed as continuous or paused and either saved on the device or on

the external storage card. The editing section allows the user to trim the beginning, ending

or both for whatever desired amount of time. Additional recordings were created and then

later edited and saved as overwritten recordings. All original, edited and overwritten

recordings were transferred to the computer using a USB cable.

Samsung S6 and S9

As previously stated in Chapter 2, the S6 and S9 had three quality settings all of

which could be done in mono or stereo: low quality, mid quality and high quality; therefore,

each set of recordings had to be completed in each quality setting, including all edited

recordings. Like the Q6, continuous and paused recordings were created. A protocol was

created to “stop” and “save” immediately after recording and “stop” is pressed and “save” is

pressed one minute later. Later, original recordings were changed by recording over a

portion of the recording and then saved as an overwritten file. Recordings were also

and USB-C cable respectively.

CHAPTER IV

RESULTS

All phones – except for the HTC One - complied to the QuickTime File Format

Specification [7]. Figure 23 is an example of a movie atom structure showing the

breakdown of the moov atom and what order the atoms are in. Each voice recording -

again with the exception of the HTC One – followed this structure.

While the S6 and S9 were almost exactly the same in Voice Recorder app and all the

features that it offered, when it came to the results that were found, they actually differed

on a few things. Therefore, each phone will be listed separately with the results that were

The HTC One revealed a minimal amount of results. One key factor noted from the

very beginning was the inability to edit directly on the app. The encoding of the audio is

also limited to AMR-NB, AMR-WB and AAC-LC. It is possible to take a recording from the

recording and the other original recordings.

When the edited recording was downloaded back onto the app, there was no visible

difference between that one and others that were directly recorded on the phone (Figure

24). The date displayed is the date that the audio was downloaded onto the phone from

the computer after it had been edited in Adobe Audition. In the list of recordings, it is listed

at the top since it was the most recent recording, but there is nothing else visually that sets

it apart from any of the other recordings.

Figure 24: Edited Audio in Voice Recorder

The recordings on this device also contained a minimal amount of metadata. When

looked at through a hex editor like 010 Editor [9], most of the data was raw audio data,

including the AAC recordings (Figure 25, Figure 26, Figure 27). Therefore, there was no

atom structure to examine.

The Android OS, like the iOS, will always be updating with new features and

abilities. The Voice Recorder app will also go through updating and possibly a total refresh

to the app. These new developments will need to be studied.

There are also audio recording apps available that can record a phone call. These,

too, need research. It is important to keep in mind with this type of recording that state

laws are taken into consideration. In some states only one party needs to be aware that the

conversation is being recorded, while others require that both parties know and consent to

having the conversation recorded.

1. Callaham, J. The History of Android OS: its name, origin and more. 2019 August 18,

https://www.androidauthority.com/history-android-os-name-789433/.

2. O'Dea, S. Android OS market share of smartphone sales to end users from 2009-2018.

https://www.statista.com/statistics/216420/global-market-share-forecast-of-

Recorded Using the "Voice Memos" App, in 2017 International Conference on Audio

5. Hill, A., ANALYSIS OF AUDIO RECORDINGS MADE USING “VOICE MEMOS”

Denver: National Center for Media Forensics.

6. Scientific Working Group on Digital Evidence, SWGDE Digital and Multimedia

https://www.swgde.org/documents/Current%20Documents/SWGDE%20Digital%

https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/Q

TFFPreface/qtffPreface.html.

8. Adobe, Adobe Audition. adobe.com.

9. 010 Editor. Sweetscape Software.