Songs to Test By is the soundtrack for Portal 2. Songs to Test By was made available free from the Portal 2 official website in .mp3 format, and a 4-disk Collectors Edition is available to purchase from Amazon.
Shorter versions of particular songs, or sound effects from the game, are available as ringtones from the website above. The soundtrack was released in three volumes: The first, titled Volume 1, was released on May 25, 2011; Volume 2 on July 1, 2011, Volume 3 on Sept. 30, 2011, and as a 4-disk Collectors Edition on October 30, 2012. Volumes 1, 2, and 3 were composed by Mike Morasky (credited as Aperture Science Psychoacoustic Laboratories) and volume 4, the soundtrack of the first Portal game, was composed by both Morasky and Kelly Bailey.
The Collectors Edition also includes in-game promotional items for Team Fortress 2, and to & in-game promotional items for Dota 2, and the Turret Lullaby comic.
Portal 2: Songs to Test By - Volume 1 (Collectors Edition Disk #1)
Album: Portal 2: Songs to Test By - Volume 1 by Aperture Science Psychoacoustics Laboratory
- Science is Fun by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [2:33] |
Download | 
Play
Played during the Portal 2 TV Spot and other trailers.
- Concentration Enhancing Menu Initialiser by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [2:33] | Download | Play
In the PS3 Menu selection when highlighting Portal 2.
- 9999999 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:11] | Download | Play
On the first main menu screen and near the end of The Escape, when viewing GLaDOS's chamber from the outside. The second half is a remix of Music Of The Spheres, containing the drum groove from Forwarding The Cause of Science and The Reunion.
- The Courtesy Call by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:37] | Download | Play
Played from when the player is first woken by Wheatley until the end of the container ride.
- Technical Difficulties by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:21] | Download | Play
Plays during The Courtesy Call in Test Chamber 0
- Overgrowth by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [2:50] | Download | Play
Plays during The Courtesy Call in Test Chamber 1
- Ghost of Rattman by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [4:06] | Download | Play
In the Rattmann chamber surrounding the Portal gun. Rattmann can be heard grunting in the background.
- Haunted Panels by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [1:36] | Download | Play
Plays in Test Chamber 5.
- The Future Starts With You by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:21] | Download | Play
Plays in Test Chamber 6.
- There She Is by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [4:20] | Download | Play
Played when walking through GLaDOS's chamber for the first time.
- You Know Her? by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:10] | Download | Play
Plays when waking GLaDOS and walking through the Incinerator. The song contains notes from Turret Redemption Line, and is remixed in Bombs For Throwing at You.
- The Friendly Faith Plate by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [2:59] | Download | Play
A chaotic electronic track that plays when being propelled through the air via a Faith plate. Starts playing when the Weighted Storage Cube is first dropped in Chapter 2 in Test Chamber 5.
- 15 Acres of Broken Glass by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [4:59] | Download | Play
The ambient, crunching synth acts as an atmospheric track for Chapter 2 Test Chamber 6, and the distorted, percussive loop plays when being propelled by faith plates.
- Love as a Construct by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [4:57] | Download | Play
Plays in Chapter 2 Test Chamber 7. When near the Companion Cube, the melody from Cara Mia Addio, the Turret Opera, can be faintly heard.
- I Saw a Deer Today by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:13] | Download | Play
Different parts of this track play when solving different parts of Chapter 2 Test Chamber 10, and the song builds on itself.
- Hard Sunshine by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [2:48] | Download | Play
An electric, buzzing, and distorted synth track, played when on a Hard Light Bridge. The song can be heard louder when crouching. The melody from Cara Mia Addio can be heard.
- I'm Different by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [4:28] | Download | Play
A melancholic, lamenting track played in Chapter 3 Test Chamber 13. The high, wailing synth melody plays when a turret is knocked over. An excerpt from this track can be heard in An Accent Beyond.
- Adrenal Vapor by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [2:36] | Download | Play
A simple, bubbly and nostalgic track, consisting only of layered sine waves, that plays in Chapter 3 Test Chamber 14. The track builds on itself, as a new layer is added each time a laser relay is activated.
- Turret Wife Serenade by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [1:38] | Download | Play
Plays when entering the Ratman den in Chapter 3 Test Chamber 16, in which the player can see four turrets, nicknamed the "Turret Quartet," singing for the Prima Donna Turret, also known as the Turret Wife.
- I Made It All Up by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:56] | Download | Play
A melodic, nostalgic track consisting of layered synths that plays in Chapter 4 Test Chamber 18. The song builds on itself as laser relays are activated.
- Comedy = Tragedy + Time by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [3:29] | Download | Play
An echoing, industrial-sounding track consisting of mechanical noises and booming clangs that plays in Chapter 4 Test Chamber 19. The song has no melody, and is more of an atmospheric track; The reverberating, hollowness of the song mirrors the spaciousness of the chamber.
- Triple Laser Phase by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By [4:15] | Download | Play
An electronic track consisting of layered synths that plays in Chapter 4 Test Chamber 20. The song builds on itself, with a new layer added each time one of the three laser receptacles is activated. When the test chamber is complete, the song's layers are all playing in unison.
- It is worth noting that the song makes use of musical dissonance.
Portal 2: Songs to Test By - Volume 2 (Collectors Edition Disk #2)
Album: Portal 2: Songs to Test By - Volume 2 by Aperture Science Psychoacoustics Laboratory
- You Will Be Perfect by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [2:39] | Download | Play
Plays in the "Meet the Bots" co-op campaign trailer. The middle is a remix of Reconstructing More Science.
- Halls Of Science 4 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [4:35] | Download | Play
Plays in the first half of Valve's TV Spot trailer for Portal 2 and in custom test chambers made in Puzzle Creator. All Robot Waiting Room tracks except 1 and 6 are remixes of it.
- Bots Build Bots by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [4:07] | Download | Play
Plays on the main menu after GLaDOS is awoken. The first part is a haunting flute and harp melody with rippling synths. The second part is a remix of Die Cut Laser Dance.
- An Accent Beyond by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [2:58] | Download | Play
Plays during the escape in Test Chamber 21. The melody of I'm Different can be heard when knocking over turrets in one of GLaDOS's traps.
- It is worth noting that the descending synth riff plays twice in the soundtrack version, once at the very beginning and again when GLaDOS opens up panels to reveal the final test chamber, with a Hard Light Bridge leading to it. However, in the game version, the riff (at the beginning and end of the album version) is only heard when GLaDOS reveals the chamber.
- Robot Ghost Story by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:07] | Download | Play
Plays when entering the Turret factory, as the player traverses static conveyors while listening to Wheatley's haunting tale.
- Die Cut Laser Dance by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [2:01] | Download | Play
An upbeat, salsa/tango style track riddled with mechanical cutting sounds. This track plays as the protagonist dodges the laser-cutting robot arms in Turret Manufacturing. This song is remixed in the second part of Bots Build Bots.
- Turret Redemption Line by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:23] | Download | Play
Plays when entering the turret redemption line. Contains notes from the second half of You Know Her?
- Bring Your Daughter To Work Day by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [2:40] | Download | Play
Plays when examining the abandoned science projects left behind from Bring Your Daughter to Work Day, when GLaDOS killed all except one of Aperture's scientists with neurotoxin gas.
- Almost At Fifty Percent by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [1:59] | Download | Play
The track starts with ambient synths and distant water-drop-like sounds, slowly becoming more electronic as the player cuts the Neurotoxin Generator's tubes. The second part of the song is a heavy, fast-paced electronic track. This plays as the generator collapses and Wheatley urges the protagonist to enter the control room and ride the exposed tube to the Central AI Chamber. The song ends with a suction sound, as Wheatley and the player are sucked into the tube. The beginning can be heard briefly at the start of Don't Do It, as well as the and of Caroline Deleted and the beginning of Cara Mia Addio.
- Don't Do It by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [5:16] | Download | Play
Plays when Chell enters GLaDOS' chamber for a second time and is required to press the Stalemate Resolution Button. This song is remixed in The Part Where He Kills You, Bombs For Throwing at You, and Your Precious Moon. The first part of Almost At Fifty Percent can be heard briefly at the beginning.
- I AM NOT A MORON! by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:46] | Download | Play
The beginning of the song is an uneasy electronic melody with alarm-like synths that plays when the core transfer is happening. The second part, an upbeat, more heavily electronic track, plays while Wheatley is marveling over his size and newfound abilities after being transferred into GLaDOS's mainframe. The third part is an increasingly dramatic orchestral piece that plays when Wheatley betrays the protagonist, delivers his villainous monologue, puts GLaDOS into a potato battery, and the player learns of Wheatley's true purpose. The song is left hanging on a single note as the player and PotatOS plummet down the elevator shaft.
- Vitrification Order by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [6:34] | Download | Play
A mighty horn track filled with dread that plays in Tartaros 9. When the player advances in the level to one of the catwalks overlooking the condemned site, the song switches to its more electronic second half.
- Music of the Spheres by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:38] | Download | Play
Plays after entering the large vault door and the player sees the Enrichment Spheres for the first time.
- You are Not Part Of the Control Group by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:24] | Download | Play
Plays during the first Repulsion Gel test. The broken chord arpeggios play when bouncing on the gel. Some of the notes in this song are featured in Robot Waiting Room 1.
- Forwarding the Cause of Science by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:40] | Download | Play
A more electronic remix of the second half of “You Are Not Part of the Control Group” which plays during later Repulsion Gel tests. The broken chord arpeggios play when bouncing on the gel.
- PotatOS Lament by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [1:59] | Download | Play
Plays on the main menu after the player has fallen into Old Aperture, from chapters 6-7.
- The Reunion by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [3:45] | Download | Play
Plays during the Propulsion Gel tests after reuniting with PotatOS. This track is an extremely electronic, distorted remix of You Are Not Part of the Control Group. Unlike Forwarding The Cause of Science, this remix maintains the tempo of You Are Not Part of the Control Group, as it is not sped up in any way. The stuttering synth arpeggios play when speeding on the Propulsion Gel.
- Music of the Spheres 2 (Incendiary Lemons) by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 2 [2:43] | Download | Play
Plays when entering Pump Station Gamma and during Cave Johnson's lemon rant. It is a heavier, more electronic remix of the second part of Music of the Spheres, with distorted, buzzing synths.
Portal 2: Songs to Test By - Volume 3 (Collectors Edition Disk #3)
Album: Portal 2: Songs to Test By - Volume 3 by Aperture Science Psychoacoustics Laboratory
- Reconstructing More Science by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:36] | Download | Play
Plays during the Portal 2 official teaser trailer. The percussion loop from this song can be heard in Caroline Deleted.
- Wheatley Science by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:29] | Download | Play
Plays during some of Wheatley's tests in Chapter 8. This song is remixed in The Part Where He Kills You, which, in turn, is remixed in Bombs For Throwing At You.
- Franken Turrets by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [4:08] | Download | Play
Plays during some of Wheatley's tests in Chapter 8.
- Machiavellian Bach by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [4:01] | Download | Play
A rendition of Johann Sebastian Bach's "Little Prelude in C minor, BWV 934," but transposed from the key of C minor to F minor. The first half is played on a harpsichord. The second half, which is the same melody but very electronic-sounding and played on synthesizers, only plays when the player is being launched by a Faith Plate or flinging themself with the use of an Excursion Funnel.
- In the game, when the player is performing one of the aforementioned actions, the second half briefly takes the place of whichever part of the first half would be playing at the time. This is one of the many examples of how composer Mike Morasky uses procedurally generated music, or music that is generated in real time based on the player's actions.
- Excursion Funnel by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [4:32] | Download | Play
Plays in Chapter 8 when the player is inside an Excursion Funnel. This is remixed in the first part of The Part Where He Kills You.
- TEST by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [6:14] | Download | Play
Plays during some of Wheatley's tests in Chapter 8.
- The Part Where He Kills You by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [3:23] | Download | Play
The first part of this song is a remix of Excursion Funnel with added percussion. This is broken by a startling synth arpeggio when the player is hurtled towards Wheatley and his "mash-y spike plates". The rest of the song is a fast-paced, electronic remix of Wheatley Science and Don't Do It. Part of this song also plays on the menu screen during Chapter 9.
- Omg, What has He Done? by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:24] | Download | Play
Plays right before entering "Wheatley's Lair," as PotatOS remarks on the disheveled state of her facility caused by Wheatley's ignorance.
- Bombs for Throwing at You by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [5:48] | Download | Play
A highly climactic track that plays during the final battle between Wheatley and the protagonist. The main melody, a remix of The Part Where He Kills You, I AM NOT A MORON!, and the second half of You Know Her, plays as Wheatley attacks the player with bombs and the player attempts to redirect them back at Wheatley. The percussive interludes play when Wheatley is stunned and the player attaches the corrupted Cores to his mainframe.
- Your Precious Moon by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [1:55] | Download | Play
Plays after all 3 corrupted cores have been attached to Wheatley. The first part, a dramatic remix of Don't Do It, plays as PotatOS urges the player to press the Stalemate Resolution Button, which turns out to be booby-trapped by Wheatley. This is broken by a comedic chime when the player shoots a portal onto the moon. The second part, an even more dramatic orchestral piece, plays as the protagonist, Wheatley, and the corrupted cores are sucked out into the vacuum of space, and GLaDOS, back in control, knocks Wheatley out of the player's hand and saves them, pulling them back through the portal with a robotic arm.
- Caroline Deleted by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [1:50] | Download | Play
Plays in GLaDOS' final talk with Chell, and the elevator ride up to the Turret Opera. The first part is a rendition of You Are Not Part of the Control Group, which is interrupted by a beep as GLaDOS supposedly deletes Caroline from her system. The second part is a rendition of Don't Do It, and the third part is a rendition of Reconstructing More Science. The song ends with the first three notes of Cara Mia Addio.
- During the third part of the song, the percussion loop from Reconstructing More Science doesn't match up with the melody. It is unknown whether this was intentional or a mistake.
- It is also unknown why the last three notes of Caroline Deleted are the first three notes of Cara Mia Addio, although its purpose was likely to make a connection between the two consecutive songs.
- Cara Mia Addio! by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:33] | Download | Play
The Turret Opera.
- The first three notes of this song are the last three notes of the previous song, Caroline Deleted. However, there are two auditory differences. First, the notes of Cara Mia Addio are much clearer and crisper than those of Caroline Deleted. Second, the turret sound effects are not present in the previous song.
- Want You Gone by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:21] | Download | Play
The Portal 2 Official Ending Song, with the first Portal game's being Still Alive.
- Spaaaaace by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [0:45] | Download | Play
Ambient ringing and space sounds. Plays during Wheatley's apology speech.
- Space Phase by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [1:32] | Download | Play
A rendition of I Made It All Up, with added strings and harmony, that plays on the final menu screen, after the player has completed the single player campaign.
- Some Assembly Required by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [1:50] | Download | Play
Plays in the co-op campaign when GLaDOS disassembles and reassembles Atlas and P-body.
- Robot Waiting Room #1 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:14] | Download | Play
Plays in the Hub during the co-op campaign. It's one of the only two Robot Waiting Room tracks that isn't used in Puzzle Creator chambers and isn't a remix of Halls of Science 4. Instead of being a remix of Halls of Science 4, it contains notes from You are Not Part Of the Control Group.
- Robot Waiting Room #2 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:14] | Download | Play
Plays in the Hub during the co-op campaign and in custom test chambers made in Puzzle Creator. It's a remix of Halls of Science 4.
- Robot Waiting Room #3 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:14] | Download | Play
Plays in the Hub during the co-op campaign and in custom test chambers made in Puzzle Creator. It's a remix of Halls of Science 4.
- Robot Waiting Room #4 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:14] | Download | Play
Plays in the Hub during the co-op campaign and in custom test chambers made in Puzzle Creator. It's a remix of Halls of Science 4.
- Robot Waiting Room #5 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:14] | Download | Play
Plays in the Hub during the co-op campaign and in custom test chambers made in Puzzle Creator. It's a remix of Halls of Science 4.
- Robot Waiting Room #6 by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [2:06] | Download | Play
Plays in the Hub during the co-op campaign. It's one of the only two Robot Waiting Room tracks that isn't used in Puzzle Creator chambers and isn't a remix of Halls of Science 4.
- You Saved Science by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [0:47] | Download | Play
An angelic track that plays when GLaDOS congratulates the bots for locating the test subjects in cryogenic storage.
- Robots FTW by Aperture Science Psychoacoustics Laboratory on Portal 2: Songs to Test By - Volume 3 [3:38] | Download | Play
An upbeat, electronic dance track that serves as the end credits theme for the co-op campaign.
Collectors Edition Disk #4
There are no downloads because it's a copyrighted disk. Mostly ambient tracks from the first Portal game, composed by Kelly Bailey and Mike Morasky.
Others
1. Exile Vilify - 4:46 by The National
Plays on the radio in the Ratmann den in Portal 2 Chapter 2 Test Chamber 3.
Ringtones
Volume 1
- Turret Wife Serenade [0:19] | Download: mp3 | m4a | m4r | Play
- Science Is Fun [0:18] | Download: mp3 | m4a | m4r | Play
- The Friendly Faith Plate [0:16] | Download: mp3 | m4a | m4r | Play
- The Courtesy Call [0:16] | Download: mp3 | m4a | m4r | Play
- I Saw a Deer Today [0:29] | Download: mp3 | m4a | m4r | Play
- Comedy Equals Tragedy Plus Time [0:29] | Download: mp3 | m4a | m4r | Play
Volume 2
Music
- Halls of Science [0:14] | Download: mp3 | m4a | m4r | Play
- Music of the Spheres [0:19] | Download: mp3 | m4a | m4r | Play
- You Are Not Part Of The Control Group [0:18] | Download: mp3 | m4a | m4r | Play
- PotatOS Lament [0:15] | Download: mp3 | m4a | m4r | Play
- You Will Be Perfect [0:13] | Download: mp3 | m4a | m4r | Play
- Bring Your Daughter To Work Day [0:15] | Download: mp3 | m4a | m4r | Play
Sound Effects
- Button Positive [0:01] | Download: mp3 | m4a | m4r | Play
- Button Negative [0:01] | Download: mp3 | m4a | m4r | Play
- Door Open [0:01] | Download: mp3 | m4a | m4r | Play
- Door Close [0:01] | Download: mp3 | m4a | m4r | Play
- Shoot Blue Portal [0:01] | Download: mp3 | m4a | m4r | Play
- Shoot Orange Portal [0:01] | Download: mp3 | m4a | m4r | Play
- Blue Paint [0:02] | Download: mp3 | m4a | m4r | Play
- Turret Machine Gun [0:01] | Download: mp3 | m4a | m4r | Play
Volume 3
- Reconstructing More Science [0:08] | Download: mp3 | m4a | m4r | Play
- Your Precious Moon [0:10] | Download: mp3 | m4a | m4r | Play
- Cara Mia Addio [0:09] | Download: mp3 | m4a | m4r | Play
- Want You Gone [0:09] | Download: mp3 | m4a | m4r | Play
- Some Assembly Required [0:06] | Download: mp3 | m4a | m4r | Play
- Robots FTW [0:09] | Download: mp3 | m4a | m4r | Play
Trivia
Please note that the Trivia section consists purely or mainly of recurring melodies. This section also may be considered as a spoiler for people who would like to listen to the OST themselves.
- Adrenal Vapor, You Are Not Part of The Control Group, Forwarding The Cause of Science, Robot Waiting Room #6 have a very similar execution and contain a pure sinewave foundation.
- The second part of 9999999 is actually a remix of Music of the Spheres I.
- The track The Courtesy Call has its first part unique to itself, the second part is a sped-up version of Music of the Spheres I and the last part is a slowed-down version of Reconstructing More Science
- Likely made to reflect on the entire game before, Caroline Deleted contains a snippet from The Courtesy Call at the very beginning, a few lines from Cara Mia Addio! right after that as well as a few looping notes from Music of the Spheres I both as deep and slow and as high-pitched and fast. The song then changes to a remix of Reconstructing More Science, ending on the buzzing noises from Don't Do It.
- Similarly, I'm Different contains a few tones from Bombs For Throwing at You. They are however hard to recognize, as an extra tone with a different frequency is added right after an original one - only the quiet melody connects it with the other track.
- Tracks playing in the underground test chambers (You Are Not Part of The Control Group, Robot Waiting Room #1, Forwarding The Cause of Science and The Reunion) are all actually edited versions of the last one, becoming more corrupt with computer errors as time progresses and more of Aperture's story is revealed.