ADR and loop group

Automated dialogue replacement, universally called ADR, is the process of re-recording an actor's lines in a studio while they watch the picture, so the new recording can replace or add to the production dialogue. It is sometimes called looping, after the old practice of cutting film into loops that ran repeatedly while actors matched their lines. ADR rescues lines ruined by noise, adds lines that clarify the story, changes performances, removes profanity for broadcast versions, and creates the off-screen voices that fill out a scene. Loop group, or group ADR, is the related craft of recording crowds, background conversations and incidental voices with a team of specialized voice actors. This lesson covers when to use ADR, how to prepare and run a session, how to make ADR match production sound, and how loop group works.

Why and when to replace dialogue

ADR has a cost beyond money: it is very hard for actors to recreate the energy and spontaneity of a performance given months earlier on set, surrounded by other actors and the real location. Many directors prefer imperfect production dialogue to a technically clean but lifeless replacement. Good production sound reduces ADR; good dialogue editing, with alts and careful repair, reduces it further. ADR is the last resort for technical problems, but it is also a creative tool.

The ADR list and cue sheets

The ADR supervisor, often working with the dialogue editor, builds the ADR list from spotting notes and the dialogue edit. Each line becomes a cue with a cue number, the character, the timecode in and out, the original line as spoken, any new wording, and the reason. Cues are grouped by actor because studio time is booked per actor. The list goes to the director for approval and then to the producers, who book the actors and the studio.

Cue numbering systems vary, but a common format combines the reel, the character and a sequence number, such as 2MAR15 for Mara's fifteenth cue in reel 2. The cue sheet given to the studio lists each cue with its timecodes and text so the ADR mixer can set up each loop quickly.

def tc_to_frames(tc, fps=24):
    h, m, s, f = map(int, tc.split(':'))
    return ((h * 60 + m) * 60 + s) * fps + f
cues = [('2MAR14', '01:14:02:10', '01:14:05:02'), ('2MAR15', '01:14:09:20', '01:14:11:08'),
        ('2DEV07', '01:14:12:00', '01:14:16:14'), ('2DEV08', '01:15:30:05', '01:15:31:20')]
total = 0
for name, tin, tout in cues:
    secs = (tc_to_frames(tout) - tc_to_frames(tin)) / 24
    total += secs
    print(f'{name}: {secs:4.1f} s')
minutes_per_cue = 5          # illustrative average for rehearsal, takes and playback
print(f'{len(cues)} cues, {total:.1f} s of dialogue; plan about {len(cues) * minutes_per_cue} minutes of studio time')

2MAR14:  2.7 s
2MAR15:  1.5 s
2DEV07:  4.6 s
2DEV08:  1.6 s
4 cues, 10.4 s of dialogue; plan about 20 minutes of studio time

Studio time per cue varies widely: a simple technical replacement may take two or three minutes, while an emotional scene with a director's notes may take twenty. A planning figure of about 10 to 15 cues per hour for straightforward technical replacement, and fewer for performance cues, is common, but supervisors adjust for each actor and director.

The ADR studio and session

An ADR stage is a quiet, acoustically controlled room, often large enough to allow different microphone distances and some movement, with a screen showing the picture and a window or camera link to the control room. The ADR mixer runs the recording system, which plays the picture and the original production line in the actor's headphones, then records new takes on demand. The director and ADR supervisor sit in the control room and give notes; the actor performs to picture.

Actors cue themselves using a sequence of audible beeps and visual streamers. The common convention is three beeps at one-second intervals, with the line beginning where a fourth beep would fall; a streamer, a vertical line moving across the screen, ends at the start of the line. Many actors prefer to listen to the original production line several times, then perform with it muted in their headphones, matching its rhythm. Some studios use rhythm-based approaches with the text scrolling over picture, a method borrowed from dubbing.

Each cue is recorded several times. The ADR mixer marks takes the director likes and the editor will later choose from, and may record a second microphone at a different distance to give the editor options for matching perspective. Multiple takes of the whole line are better than piecing words together later, though editors routinely combine the best parts of several takes.

In Canada, performers recording ADR on productions covered by an ACTRA agreement, such as the Independent Production Agreement, are paid and scheduled under that agreement's rules for post-production sessions. Producers and supervisors should check the current agreement before booking sessions.

Remote ADR

Remote ADR sessions, in which the actor records in a studio or a well-treated room in another city while the director and supervisor listen online, became routine during the pandemic years and remain common. Low-latency streaming tools carry picture and audio between locations, and the remote studio records the high-quality files locally for upload. Remote sessions save travel and allow actors on other productions to record between commitments, but they require careful planning: matched microphones where possible, a reliable connection, a local engineer, and a test session to check sound and timing.

Making ADR match

The hardest part of ADR is making it sound as if it were recorded on set. A studio recording is clean, close and dry; the production recording carries the room's reflections, the location's background, a particular microphone and distance, and the actor's physical state, such as walking, running or lying down. Matching starts in the session and continues in editing and mixing.

In the session, the ADR mixer chooses a microphone similar to the production boom, often the same model, and places it at a similar distance and angle. Actors are encouraged to move as they did on set: walking on the spot, holding a prop, lying on a couch. Energy matters: a line shouted across a field must be performed with the same effort, not just the same volume. The production line is played before each take so the actor can match pitch and rhythm.

In editing, the ADR editor syncs each take to picture, adjusting individual words and syllables by a few frames with time-stretching tools when needed, and checks lip sync on close-ups. In mixing, the re-recording mixer applies equalization to match the production microphone's tone, adds reverberation that matches the location, often using impulse responses recorded on set, and lays production room tone underneath so the ADR line sits in the same background as the lines around it.

Loop group and walla

Loop group is a team of voice actors who record the voices of crowds, background characters and incidental dialogue: restaurant chatter, hospital announcements, police radio, reactions in a courtroom, children in a playground. Walla is the term for indistinct crowd murmur; the name comes from the old practice of actors repeating "walla walla" to create a murmur without intelligible words. Modern loop groups do much more than murmur. They research the setting and improvise period-appropriate, culturally accurate and story-specific dialogue, because audiences notice when background voices say the wrong thing.

A loop group session might record a busy restaurant in several layers: general murmur from the whole group, small groups of two or three at specific tables matching people visible in the shot, a waiter's lines, cutlery reactions and laughter. Specific lines that can be heard clearly may need clearance: they must not include real names, real phone numbers or brands without permission, and they must match the film's rating and broadcast standards. Loop group performers also provide efforts, the breaths, grunts and exertion sounds of characters in fights and action, when the principal actors cannot.

Language, accents and authenticity

Background voices must be authentic to the setting. A scene set in Montreal may need French and English walla with appropriate accents; a scene in a Toronto market may need several languages; a scene in a New Orleans club may need voices that fit the region. Loop group coordinators cast performers who speak the languages and dialects needed and research what people would plausibly say. Inauthentic or stereotyped background voices can undermine a film's credibility and offend the communities depicted. Where real languages are used, check the content with fluent speakers.

Canadian productions often need French and English loop group versions and, for some projects, Indigenous languages, which call for consultation with the relevant community and fluent speakers.

Editing and delivering ADR

ADR editors cut the chosen takes into the dialogue session on dedicated ADR tracks, keeping the original production lines muted underneath for comparison. Loop group is edited on its own tracks, often by a separate editor, and organized so the mixer can control density. ADR and loop group are delivered as part of the dialogue stem, because they are speech. For the music and effects version used in dubbing, background walla in a foreign language may be kept or removed depending on whether it is part of the setting; specifics are set by the distributor's deliverable requirements.