Comparing Movie Sound Quality when Played as Stereo vs Multichannel

[Fredygump]

I want to ask a specific question about the mixing and mastering of different types of recordings. But it's a difficult question to ask without getting super sidetracked!

If a movie has both stereo and multichannel audio, is there going to be noticeable audio quality difference between the two? If the stereo version is played on a 2.1 system, and the multichannel recording is being decoded and played on a 2.1 or 3.1 system? Both are being played on the same equipment, the capability of equipment is not a variable.

Generally speaking:

Is the stereo mix more compressed, or the same?
Is LFE baked into the stereo mix, or is LFE going to be missing from the stereo mix?


I was watching a few movies recently, and I noticed that the audio on many movies seems lacking. Admittedly most of these were streaming, but it was true of my The Matrix Blueray as well. But occasionally a streaming movie seems to have very good sound quality in stereo.

Would I get different results if I had an AVR/processor that is decoding the multichannel audio these movies were created with? Or am I just observing the variation in the quality of movie audio?

 

[MRC01]

It depends on the movie. Not all movies have a 2-channel mix. But when they do, often it is dynamically compressed or otherwise processed to make it easier to listen to in compromised situations - whether sub-optimal environments or equipment. That's not the mix I want to listen to on my optimal equipment in my optimized listening room. I like wide uncompressed dynamics and natural lifelike sound without the mid-presence lift often applied to make dialog easier to hear.

With streaming, transmission protocols and formats vary, but it is always significantly compressed because the bandwidth is limited. They optimize for picture quality rather than audio, as that what most people will notice (big screens & small speakers). DVD and BluRay are also compressed, but relatively speaking they are less compressed than streaming. And they have better sound quality than streaming.

All that said, I have old fashioned 2 channel stereo. The standard audio track made for multichannel is not optimized for this, but I find it usually sounds better than the alternatives (relatively speaking).

Just my experience & opinion, FWIW.

 

[Fredygump]

Gonna bump my thread, 'cause it is still the $5000 question! (That is, it costs $5,000 to buy a processor to find out if a processor actually makes a difference...)

The reason I am asking again is because I am debating on subwoofer design choices. Choice is to sacrifice 5dB of output for flat to 20hz extension, or gain 5dB and tune to 25hz to achieve THX reference level...with an f3 of ~25hz. The prototype iterations I have are 20hz capable, and it really isn't clear if it matters!

It's really a silly debate.....it's 5dB or 5hz. Probably it won't ever matter either way. Audio doctrine says to get 20hz extension, because it exists. But on the other hand, peak SPL on the frequencies we can clearly hear seems to be a more practical choice. I noticed Genelec chose higher SPL with a higher tuning over 20hz extension in their 8381A...interesting choice? I don't know if that's because they are more clever than we are? It seems silly to suggest adding a subwoofer to the genelec system to cover 20-25hz! (I believe it has an F10 of 20hz)

Part of me wants to believe people when they talk about the importance of 20hz and infrasonic capable subwoofers, but to be honest, I'm kind of wondering how much of that is legit. Over the internet it is not always clear if people are experiencing infrasonics, or if these subs are just really loud at 30hz? 30hz at high SPL can get exciting with things rattling and moving around! But it seems that about the only time I have 20hz frequencies shaking things in my house is when I run sweeps to measure my system.... (insert sad face?)

 

[Audionaut]

Yes, I would say there can be a noticeable difference in sound quality between a movie’s stereo mix and its multichannel version, even when both are played on the same device using a 2.1 or 3.1 audio system. Multichannel soundtracks—such as 5.1 or 7.1 mixes—often provide better clarity, more spatial depth, and greater dynamic range. Even when they’re downmixed to fewer channels, the result tends to sound more immersive and balanced than the native stereo mix.

This is mainly because multichannel audio separates sound elements into distinct channels. Dialogue, for example, is placed in the center channel, while music and effects are spread across the others, and deep bass effects are handled by a dedicated LFE (Low Frequency Effects) channel. When downmixed, this separation helps preserve detail and directionality, and on a 3.1 system, having a real center channel significantly improves speech intelligibility.

Stereo mixes, by comparison, are often more compressed—both in terms of audio dynamics and data rate. They usually combine all elements into the left and right channels, which can make the soundstage feel narrower and more congested. Especially on streaming services, the stereo track is typically more heavily compressed to save bandwidth and is optimized for basic playback devices like TVs or laptops.

Another important difference is bass management. Stereo tracks don’t include a separate LFE channel. Instead, low frequencies are embedded in the main left and right channels, and the system’s bass management splits them off for the subwoofer. This is less precise than the dedicated LFE channel found in multichannel formats, which can deliver cleaner, more impactful low-end effects.

As for data rates, modern surround formats vary widely. Standard Dolby Digital uses a lossy compression scheme and typically ranges between 384 and 640 kilobits per second. DTS, another common format, usually ranges from 768 to 1509 kilobits per second, also lossy. A step up from these is Dolby Digital Plus, which can deliver up to around 6 megabits per second and is widely used by streaming platforms for 5.1 and 7.1 sound. For the best quality, lossless formats such as Dolby TrueHD and DTS-HD Master Audio are used on Blu-rays; they support bitrates of up to approximately 18 and 24.5 megabits per second, respectively. Finally, LPCM (Linear PCM), which is uncompressed audio, can reach even higher rates—up to 27 megabits per second on Blu-ray discs.

In summary, even when using a 2.1 or 3.1 system, the multichannel mix usually provides superior audio performance due to better separation, less compression, and a more detailed sound field. Whenever available, it's generally the better choice over the stereo version, especially if sound quality and immersion are important to you.

 

[Audionaut]

Part of me wants to believe people when they talk about the importance of 20hz and infrasonic capable subwoofers, but to be honest, I'm kind of wondering how much of that is legit

20 Hz makes sense, but is technically difficult to implement in normal living rooms.
To radiate 20 Hz cleanly, you need a large cone area, a large excursion of the woofer and yet low distortion.
You also need high amplifier power and tuning to the room in question.

Feasible, but not easy.
That's why we usually limit ourselves to the contra octave instead of the subcontra octave, which is technically easier to implement - and covers approx. 97% of the program material.

The full range of human hearing spans roughly from 20 Hz to 20,000 Hz (20 kHz). This range can be divided into octaves, where each octave represents a doubling of frequency.

The subcontra octave begins at around 16 Hz and extends to 32 Hz. These are the lowest frequencies, often more felt than heard. They appear in pipe organs, cinematic sound design, and electronic music for powerful low-end effects.

Next is the contra octave, ranging from 32 Hz to 64 Hz. This is where you find the deep tones of instruments like the double bass or the lowest keys on a grand piano. It provides the foundational weight in music.

The great octave spans 64 Hz to 128 Hz and contains essential bass frequencies found in kick drums, bass guitars, and low toms.

The small octave runs from 128 Hz to 256 Hz. This is where the lower midrange begins, covering the fundamental tones of many male voices and deeper instruments.

The one-lined octave covers 256 Hz to 512 Hz, including many musical fundamentals and forming a key part of the tonal body of acoustic instruments.

The two-lined octave ranges from 512 Hz to 1024 Hz (1 kHz). This upper midrange area is crucial for clarity and speech intelligibility.

The three-lined octave lies between 1 kHz and 2 kHz, and the four-lined octave spans 2 kHz to 4 kHz. These areas contain many upper harmonics and strongly affect the presence and definition of vocals and instruments. Human hearing is especially sensitive in this range.

The five-lined octave runs from 4 kHz to 8 kHz, containing very high overtones that contribute to the brightness and brilliance of sound. However, excessive energy here can sound harsh or piercing.

Finally, the six-lined octave stretches from 8 kHz to 16 kHz, and the range from 16 kHz to 20 kHz—while not a full octave—is still part of the uppermost audible spectrum. These frequencies add "air" and shimmer to audio, although they carry little tonal weight. They are mostly perceived by younger listeners with healthy hearing.

The key point is that an octave is defined by a doubling of frequency, not by a fixed number of hertz. Each octave represents a ratio of 2:1. So for example:

From 16 Hz to 32 Hz is one octave (16 × 2 = 32),

From 32 Hz to 64 Hz is another octave,

And from 8 kHz to 16 kHz is also one octave.

Even though the higher octave spans 8000 hertz in absolute terms — compared to just 16 hertz in the subcontra octave (16–32 Hz) — they are musically equal in width, because both represent a doubling in frequency. This can feel counterintuitive at first, because as frequencies rise, each octave contains more hertz numerically. But the human ear perceives pitch on a logarithmic scale, not a linear one. That means we hear equal ratios (like doubling) as equal steps in pitch.

For example, going from 100 Hz to 200 Hz sounds like the same size pitch jump as going from 1,000 Hz to 2,000 Hz — even though the second jump spans ten times more hertz. That’s because our perception is based on the relative change, not the absolute number of hertz.

This is also why musical instruments, EQs, and audio processors are designed around logarithmic frequency behavior: doubling the frequency always equals one octave, no matter where you start.

So, to answer your question: the last octave (e.g., 8 kHz to 16 kHz) contains more hertz numerically, but not more musical "space" than the first octave (e.g., 16 Hz to 32 Hz). Each octave is equally wide in musical terms, because our hearing interprets frequency proportionally.

So yes, subcontra octave from 16hz to 32 Hz is very useful, but difficult to implement and corresponds approximately to the musical information in the upper frequency range from 16khz (8khz?)

You always have to decide for yourself what is important to you.

I myself have no problem with a well-reproduced 30 Hz to 16 kHz.

 

[Fredygump]

20 Hz makes sense, but is technically difficult to implement in normal living rooms.
To radiate 20 Hz cleanly, you need a large cone area, a large excursion of the woofer and yet low distortion.
You also need high amplifier power and tuning to the room in question.

Feasible, but not easy.
That's why we usually limit ourselves to the contra octave instead of the subcontra octave, which is technically easier to implement - and covers approx. 97% of the program material.

The full range of human hearing spans roughly from 20 Hz to 20,000 Hz (20 kHz). This range can be divided into octaves, where each octave represents a doubling of frequency.

The subcontra octave begins at around 16 Hz and extends to 32 Hz. These are the lowest frequencies, often more felt than heard. They appear in pipe organs, cinematic sound design, and electronic music for powerful low-end effects.

Next is the contra octave, ranging from 32 Hz to 64 Hz. This is where you find the deep tones of instruments like the double bass or the lowest keys on a grand piano. It provides the foundational weight in music.

The great octave spans 64 Hz to 128 Hz and contains essential bass frequencies found in kick drums, bass guitars, and low toms.

The small octave runs from 128 Hz to 256 Hz. This is where the lower midrange begins, covering the fundamental tones of many male voices and deeper instruments.

The one-lined octave covers 256 Hz to 512 Hz, including many musical fundamentals and forming a key part of the tonal body of acoustic instruments.

The two-lined octave ranges from 512 Hz to 1024 Hz (1 kHz). This upper midrange area is crucial for clarity and speech intelligibility.

The three-lined octave lies between 1 kHz and 2 kHz, and the four-lined octave spans 2 kHz to 4 kHz. These areas contain many upper harmonics and strongly affect the presence and definition of vocals and instruments. Human hearing is especially sensitive in this range.

The five-lined octave runs from 4 kHz to 8 kHz, containing very high overtones that contribute to the brightness and brilliance of sound. However, excessive energy here can sound harsh or piercing.

Finally, the six-lined octave stretches from 8 kHz to 16 kHz, and the range from 16 kHz to 20 kHz—while not a full octave—is still part of the uppermost audible spectrum. These frequencies add "air" and shimmer to audio, although they carry little tonal weight. They are mostly perceived by younger listeners with healthy hearing.

The key point is that an octave is defined by a doubling of frequency, not by a fixed number of hertz. Each octave represents a ratio of 2:1. So for example:

From 16 Hz to 32 Hz is one octave (16 × 2 = 32),

From 32 Hz to 64 Hz is another octave,

And from 8 kHz to 16 kHz is also one octave.

Even though the higher octave spans 8000 hertz in absolute terms — compared to just 16 hertz in the subcontra octave (16–32 Hz) — they are musically equal in width, because both represent a doubling in frequency. This can feel counterintuitive at first, because as frequencies rise, each octave contains more hertz numerically. But the human ear perceives pitch on a logarithmic scale, not a linear one. That means we hear equal ratios (like doubling) as equal steps in pitch.

For example, going from 100 Hz to 200 Hz sounds like the same size pitch jump as going from 1,000 Hz to 2,000 Hz — even though the second jump spans ten times more hertz. That’s because our perception is based on the relative change, not the absolute number of hertz.

This is also why musical instruments, EQs, and audio processors are designed around logarithmic frequency behavior: doubling the frequency always equals one octave, no matter where you start.

So, to answer your question: the last octave (e.g., 8 kHz to 16 kHz) contains more hertz numerically, but not more musical "space" than the first octave (e.g., 16 Hz to 32 Hz). Each octave is equally wide in musical terms, because our hearing interprets frequency proportionally.

So yes, subcontra octave from 16hz to 32 Hz is very useful, but difficult to implement and corresponds approximately to the musical information in the upper frequency range from 16khz (8khz?)

You always have to decide for yourself what is important to you.

I myself have no problem with a well-reproduced 30 Hz to 16 kHz.

Now it sounds like a challenge!

The design I have been wrestling with uses a 12" sub driver. The simulation gives a max SPL of 110dB @ 20hz (F3 = 17hz), and there will be a pair of them. I have two mismatched prototypes that do achieve this goal, but neither are quite right.

Making subs with this 20hz performance would be easy if I was just making a normal subwoofer. But the challenge is that these "subs" are part of a 4 way active speaker. I'm limiting the exterior volume to ~7.7 cubic feet per tower (12" subwoofer, 12" woofer, 12" coaxial.) With the available cabinet volume, I need a long port, l think ~40" long to get enough cross sectional area to minimize port compression. The prototype is 52" tall, so technically I have enough length for a mostly straight port. But making it fit in the cabinet in a way that makes sense is the challenge!

If I were choosing the higher tuning frequency, there would be less pressure to solve the port design problem.

It is also fun to think about the possibility choosing the higher tuning, and then augmenting the lowest frequencies with a single 18" (?) subwoofer.

But the idea that inspired me to start designing my speakers was to create an "all in one" speaker that does not need extra subwoofers! So I kind of want them to achieve THX reference levels of 115dB down to 20hz. But the drivers I have won't give me both the 115dB and the 20hz at the same time.

But as a consolation, I am having success doing multiple subwoofer optimization techniques with the four woofers/ subwoofers in my active speakers, which is fun. But it isn't proven to work anywhere outside of my living room...

 

[Chrispy]

Gonna bump my thread, 'cause it is still the $5000 question! (That is, it costs $5,000 to buy a processor to find out if a processor actually makes a difference...)

The reason I am asking again is because I am debating on subwoofer design choices. Choice is to sacrifice 5dB of output for flat to 20hz extension, or gain 5dB and tune to 25hz to achieve THX reference level...with an f3 of ~25hz. The prototype iterations I have are 20hz capable, and it really isn't clear if it matters!

It's really a silly debate.....it's 5dB or 5hz. Probably it won't ever matter either way. Audio doctrine says to get 20hz extension, because it exists. But on the other hand, peak SPL on the frequencies we can clearly hear seems to be a more practical choice. I noticed Genelec chose higher SPL with a higher tuning over 20hz extension in their 8381A...interesting choice? I don't know if that's because they are more clever than we are? It seems silly to suggest adding a subwoofer to the genelec system to cover 20-25hz! (I believe it has an F10 of 20hz)

Part of me wants to believe people when they talk about the importance of 20hz and infrasonic capable subwoofers, but to be honest, I'm kind of wondering how much of that is legit. Over the internet it is not always clear if people are experiencing infrasonics, or if these subs are just really loud at 30hz? 30hz at high SPL can get exciting with things rattling and moving around! But it seems that about the only time I have 20hz frequencies shaking things in my house is when I run sweeps to measure my system.... (insert sad face?)

Is this a question about the sub's capabilities or your pre-pro? Likely it's not the pre-pro with most modern gear. An f3 of 25hz is not great sub performance....

 

[Fredygump]

Is this a question about the sub's capabilities or your pre-pro? Likely it's not the pre-pro with most modern gear. An f3 of 25hz is not great sub performance....

I currently have the capability to reproduce everything down to 20hz and a bit below, but that capability is not being utilized with the content I have access to. This applies to both bluray and streamed, although my experience is limited to the stereo version...

The reason why these soundtracks are missing the sub-30hz low frequency content is unclear. Two possibilities: either it was never actually there, or it is locked inside a proprietary format that costs thousands to unlock.

If I use movie theater experiences as my reference, I would conclude that movie sound tracks are rolled off at ~30hz. (I understand that sub-30hz frequencies would create challenges for the theater in terms of isolating theater rooms from each other, so there is a good argument for why the theater doesn't have earth shaking low frequencies.)


The answer to this question about "actual" movie soundtrack frequency range will help inform the design decisions that I described above.

 

[Chrispy]

I currently have the capability to reproduce everything down to 20hz and a bit below, but that capability is not being utilized with the content I have access to. This applies to both bluray and streamed, although my experience is limited to the stereo version...

The reason why these soundtracks are missing the sub-30hz low frequency content is unclear. Two possibilities: either it was never actually there, or it is locked inside a proprietary format that costs thousands to unlock.

If I use movie theater experiences as my reference, I would conclude that movie sound tracks are rolled off at ~30hz. (I understand that sub-30hz frequencies would create challenges for the theater in terms of isolating theater rooms from each other, so there is a good argument for why the theater doesn't have earth shaking low frequencies.)


The answer to this question about "actual" movie soundtrack frequency range will help inform the design decisions that I described above.

Movie soundtracks vary. Seems lately there's more a move to cut the infrasonic content, tho. Movie theaters generally aren't geared for infrasonic content, sometimes the better way to go was the disc. Streaming seems to be getting more compromised in levels lately.

 

[posvibes]

It depends on the movie. Not all movies have a 2-channel mix. But when they do, often it is dynamically compressed or otherwise processed to make it easier to listen to in compromised situations - whether sub-optimal environments or equipment. That's not the mix I want to listen to on my optimal equipment in my optimized listening room. I like wide uncompressed dynamics and natural lifelike sound without the mid-presence lift often applied to make dialog easier to hear.

With streaming, transmission protocols and formats vary, but it is always significantly compressed because the bandwidth is limited. They optimize for picture quality rather than audio, as that what most people will notice (big screens & small speakers). DVD and BluRay are also compressed, but relatively speaking they are less compressed than streaming. And they have better sound quality than streaming.

All that said, I have old fashioned 2 channel stereo. The standard audio track made for multichannel is not optimized for this, but I find it usually sounds better than the alternatives (relatively speaking).

Just my experience & opinion, FWIW.

"All that said, I have old fashioned 2 channel stereo. The standard audio track made for multichannel is not optimized for this, but I find it usually sounds better than the alternatives (relatively speaking)."

That seems to be my experience too, when I have been impressed with a movie soundtrack I will go looking for the recorded version on a streamer, or as I often used to do, look for a CD of the original soundtrack. And I have, in most cases, been disappointed, they always sound thinner, less full bodied than the DVD or Blu-ray version of the same music.

 

[KenMasters]

I don't think there's a one size fits all answer to the question - it really depends on the movie and format.

On catalogue titles it's common to have multiple soundtrack options which are indeed all different. There might be a more recently produced Atmos mix, along with stereo, 4ch or mono mixes depending on how they were originally presented in cinema.

In the case of more recent productions, I would think in most cases whether Atmos, 7.1, 5.1 or 2.1, you're listening to the same mix remapped as per system configuration.

As for the technical specs of the mix, while I'm aware that Dolby, DTS etc have documented recommendations, I would imagine it varies across studios and individuals.