Exposition 7

In order to minimise the difference in quality between the surround headphones and the stereo headphone i have made sure they are both of equal build quality and price range.

Other information that will be provided in my exposition will include some of the overall results from my tests and also research images.

Allan blumleins drawings of a stereo system in 1931

5.1 surround system

Also will provide an explanation how the surround headphones only utilises one cue for direction in the human hearing HRTF and that a full 5.1 system creates better localisation. However, surround headphones are used in the exhibition because headphones a popular playback medium that people will be familiar with. 

Glossary of Terms

Effects

Automation: This is the effect of creating events that will happen automatically when you play back the audio. For instance, automation can be used on the volume of a sound while it is playing so it automatically gets louder or softer. It can also be used in combination with panning to create the effect of sound sources moving around the speaker array and any other effects.

Compression: An effect used to reduce the dynamic range of a sound

Delay: An effect which stores a sound and then replays it over a period of time.

Equalisation: This is an effect used to alter the frequency range of a sound. It allows you to either cut or boost a set of frequencies, for example, if a sound contains too much "bass" or lower frequencies then they can be reduced using equalisation. 

Limiting: Is an extreme form of compression which limits all signals above the threshold to the same gain, rather than smoothly reducing it. 

Optimum Gain Signal: This is not an effect but rather how to record sounds at an optimum level. If a gain structure is too low then noise begins to be introduced to the sound. If a gain signal is too high then the sound will begin to distort. An optimum gain signal for recording audio is around 0dB, this is high enough to not introduce noise and allows enough headroom so the sound will not distort. 

Panning: Is the spread of a sound signal into a multichannel or stereo sound field. In other words panning allows you to place sounds around the speaker array, whether it be directly coming from one speaker or between speakers creating a phantom image. 

Reverb: is an effect which simulates a component of sound that consists of the reflections of the sound bouncing of the walls or objects in a room. In other words it is a room simulator. The reverberation of a room depends on many different factors:

Early Reflections - The first reflection of a sound off an object/wall that reaches the listener's ear milliseconds after the direct sound does. Early reflections enable the listener to quickly determine room size.

Reverb time - A larger enclosed space produces a larger reverb time. However a larger reverb time requires a louder source sound to allow the sound enough energy to be reflected around a large space.

Absorption - When a sound reflects of a wall/object some of the sound is absorbed into the material that the wall/object is made of. Different materials absorb different ranges of frequencies as high frequency have a smaller wavelength than lower frequencies. The greater the absorption in the room equals a smaller reverb time. 

Human Hearing

Localisation and Direction:

Inter-aural Time Differences (ITD) - This is one of the cues that helps humans perceive direction of sound, it is the difference in the time of arrival of a sound between the two ears. If a sound is coming from a source on the left then it will arrive at the left ear before the right and it is this difference in time that helps the brain determine the direction of a sound. 

Inter-aural Intensity Differences (IID) - This is another cue that helps humans perceive direction of sound, it is the difference in intensity of a sound between the two ears. If a sound is coming from a source on the left then it will be louder in the left ear than the right and it is this difference in intensity that helps towards the localisation of sound. 

Head Related Transfer Function (HRTF) - Is the way in which sound waves physically interact with the human ear. The shape of the outer ear, including parts such as the pinna, helps to direct sound into the ear canal. The differences in the physical interaction of a sound wave between the ears alongside IID and ITD is how humans localise sound sources.

Physical Factors of Sound

Amplitude - the maximum deviation of the pressure waveform from the average, unit N/m squared.

Frequency and Pitch - Frequency is the number of cycles that a sound waves make per second and is measured in Hertz. The higher the number of cycles (frequency) equals a higher pitch. The human hearing is capable of hearing from 20Hz to 20,000 Hz, however damage to hearing may cause this range of frequencies to be smaller.

Phase - Time or angular difference between one signal an another.

Resonance - The vibration of an object or medium at a specific frequency.

Velocity - The speed of time in air under normal conditions is 340m/s.

Wavelength - The length of the physical wave in metres.


Measurement of Sound:

Intensity - The "concentration" of sound, unit N/m squared or Watts/m squared.

Loudness - The subjective "measure" of SPL and has the unit phon.

Sound Pressure Level - Sound can be described as variations in air pressure, SPL uses the unit dB. SPL is a ratio between the actual sound pressure and a reference level usually the threshold of human hearing. 

Propagation of Sound:

Diffraction - Sound bends easily around obstacles that are of a similar size or smaller than the wavelength of the sound. Lower frequencies bend/diffract more freely around obstacles because of their longer wavelength.

Humidity - This has the decreasing the velocity of a sound. Dry air absorbs more energy than moist air, thus attenuates the sound to a greater level. 

Pressure - Air pressure has little effect on the velocity of sound. 

Refraction - When sound travels from a less dense medium to a more dense medium it bends in towards the normal. When it travels from a more dense medium to a less dense medium it bends away from the normal. 

Temperature - The speed of a sound increases at around 0.6m/s for every degree rise in temperature. 

Super Audio Compact Disc (SACD)

The super audio CD has been available since 1999 and is a dual-layer disc that offers 16-bit stereo, which is used for conventional CD’s and also a high-resolution six-channel mix. The benefit to this CD is that it can be played through normal CD players, however in order to playback the SACD in surround the consumer must use a SACD player or DVD player that supports SACD.

This format is precisely what the music industry needs if the 5.1 surround sound system was to become a popular playback format for music reproduction: a medium which can playback normal stereo material but also surround sound material. However, this compact disc is used rarely in the music industry. Jack schofield (2007) from the Guardian Newspaper states some interesting findings while investigating this subject in more depth:

"The International Federation of the Phonographic Industry (IFPI) says only 2m SACDs were sold last year (2006), compared to 1.7bn CDs. (This may understate sales, because IFPI doesn't track hybrids separately, and almost all SACDs are now hybrids. But how would we know if buyers were going to play the SACD layer?)"

Even though the IPFI do not track hybrids, which are both CD and SACD, the sales figures for non-hybrid SACD's are incredibly low compared to CD, especially considering these figure were taken seven years after its release. It can be seen from this that the SACD is failing to become the new standard medium for storing music. There are a few reasons as to why the release of this new compact disc was not successful. 1999, was the same year that peer-to-peer file sharing service Napster began, this allowed people to acquire music for free and share it via MP3 files. Although this service was shut down in 2001 due to the copyright infringement it was causing, many other internet based services would take its place and begin the uprising of music piracy. 

The SACD was competing in a battle that it couldn't win. Two new ways of acquiring music were available to the public, both released in the same year. One where the consumer could access their music for free via low quality MP3 files which could be stored on your computer in mass quantities. And the other a compact disc, which would still cost the consumer money and they might even have to purchase a new playback system to enjoy the high quality surround sound that it can offer. When faced with this choice, the consumer is obviously going to choose the option where they can access their music for free. Unfortunately this is obviously had a detrimental affect on the fate of the Super Audio Compact Disc. 

Difference in mastering for surround

Mastering is the process taken after the mixing stage and is the last process taken before the audio is ready for the market place. Mastering engineer’s will often compress and equalise all of the tracks for the album or E.P. to ensure that they all have a suitable dynamic and frequency range: this allows continuity from song to song. After this is done, the engineer will encode the audio to an appropriate format and this is where 5.1 and stereo music differs.

Unlike stereo in order for the consumer to be able to playback surround audio it must go through a different encoding process, this is due to the extra four channels that 5.1 surround sound utilises. Two common formats are used for encoding 5.1 audio are the Dolby Digital format (AC3) by Dolby Laboratories Inc. and DTS by Digital Theatre Systems Inc. AC3 by Dolby Labs is the mandatory format for DVD-V discs and can be encoded at up to 448kbps at a maximum resolution of 24-bit and 48kHz. Its alternative DTS can be encoded at up to 1536 kbps at a maximum resolution of 24-bit and 96kHz. These file formats have a greater resolution than CD quality (16-bit, 44.1kHz); this is because they were design for DVD purposes like film.

Although these formats were designed for DVD there is an audio CD that can replay surround audio, which is the Super Audio Compact Disc (SACD). This dual-layer disc offers 16-bit stereo, which is used for conventional CD’s and also a high-resolution six-channel mix. The benefit to this CD is that it can be played through normal CD players, however in order to playback the SACD in surround the consumer must use a SACD player or DVD player that supports SACD. 

Creation of 5.1 mixes

In order to begin re-mixing stereo material to 5.1, the stereo material must first be analysed. As mentioned before the stereo material was sourced from two different local artists from contrasting genres. Each artist provided the individual tracks of their songs and any subsequent information, such as reverb effects settings. Effects such as reverb are used different in the 5.1-system due to the extra channels; a more in-depth discussion of this can be found on the previous blog link "differences in mixing for surround"

The analysis of the stereo material provided a basis for the 5.1 material: it is important not to stray too far from the original material in order to maintain the original “sound” of the artists’ work. Although it is important to maintain the originality of the artist’s work, the whole point in re-mixing the material in 5.1 surround sound is to provide a different listening experience: one that surrounds the listener in the music creating a more immersive experience. It is for this reason that no extra effects were added that were not in the original stereo mix. However, some that were in the original were utilised differently in the 5.1-mix but maintaining the overall original sound. 

The main steps taken during the re-mixing of the stereo material were panning and pan automation. As the 5.1-system has extra rear, centre and subwoofer channels that stereo does not, the original panning methods employed in the stereo version were changed:

• Instruments that would normally be panned evenly between the left and right speakers to create a phantom centre image, such as kick and snare drums, bass instruments and vocals, were panned to directly to the centre speaker of the 5.1-system. Alongside this any bass instruments would be sent to the low-frequency enhancement channel (subwoofer).

• The lead instruments in each song, for example the piano’s in Griff’s The 2^nd Before and the mandolin in Rhauri Campbell’s instrumental, would no longer be panned to precise positions but move across speaker channels in left-to-right motion or front-to-back. This was done to exploit the 5.1 medium’s ability to reproduce better directionality and localization of sound sources. Not only this, but the moving sound sources were used in a way to create a better sense of interaction between the listener and the music, by forcing the listener to concentrate more on lead instruments and attempting to create a greater sense of involvement.

• Other instruments used as ornaments, such as the extra percussive instrumentation in Griff’s The 2^nd Before and also backing instruments such as the melodica in Rhauri Campbell’s instrumental, would be panned to the rear speakers. This would be used to create a sense of surprise when these instruments would fade in and out throughout the songs. Normally these instruments would be used to emphasise other main instruments and would be relatively low in the mix. However, because the 5.1 system eliminates problems such as masking while mixing (discussed in more depth in the blog link provided) these pieces of instrumentation can be heard more clearly and can be used more extravagantly in the mix without interfering with the main instrumentation.

Overall, the main aim while producing these 5.1 mixes was to create a more interesting and immersive listening experience without straying too far from the original. In order to maintain the original “sound” of the instrumentation, no new effects were added that would change their character. This would create continuity between the stereo and 5.1 mixes even though they both create different listening experiences. So, if no new effects were to be added to ensure continuity, that left only one way to create a more interesting and immersive listening experience, which was panning and pan automation. These methods would allow the placement of instrumentation all around the listener and allow the movement of lead sound sources to create a more exciting listening experience to concentrate upon. 

Questionnaire

This is the questionnaire that i produced and i have had 69 people fill it out, the results will be on a separate post:

Thank you for taking the time to complete this questionnaire. The answers you provide for the following questions will form part of a research project studying the listener’s preference between 5.1 surround sound and stereo music. If you have any queries about this questionnaire please contact:

Rory Bennett at 1101000@live.abertay.ac.uk

Occupation: __________________________

Please circle your answers to the following questions:

1. Do you own a 5.1 Surround Sound system?

Yes / No

2. If no, would you ever consider purchasing one?

Yes / No

3. If no again, why do you NOT want to purchase a 5.1 surround sound system?

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4. If you do own a 5.1 surround sound system what kind of media do you use it most for? (Please circle a MAXIMUM of 3 answers)

Games / Film / Television / Radio / Music

5. Do you own any music material that is in 5.1 surround sound format?

Yes / No / Don’t Know

6. Given the choice would you rather listen to your music in 5.1 surround or stereo and why?

Stereo / 5.1 surround sound

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7. How do you currently purchase/access most your music?

Download / Streaming / CD / Radio

8. How do you currently listen to the majority of your music? E.g. Ipod etc.

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