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QuickTime Music Architecture (QTMA)

The following enhancements and support for new formats in QTMA are included in QuickTime 5. Some of the known issues and limitations are also discussed in this section.

In this section:

Improved QuickTime Music Synthesizer
New Reverb to Improve Sound Quality
Updated Music Control Panel
Other Improvements
Some Limitations of Sound Font 2 and DLS Files
Assigning Custom Sound Banks to Movies

Improved QuickTime Music Synthesizer

The QuickTime Music Synthesizer, whose performance and quality of synthesis rendering has been enhanced in QuickTime 5, will support the following new formats:

• Downloadable Sounds (DLS), an industry standard which is used by MPEG-4.

• Sound Font 2 (SF2).

DLS is a sample bank format that describes to the QuickTime Music Synthesizer that you have a particular sample that responds to a particular instrument number that should be used for a range of keys and for a range of velocities, and describes the envelope characteristics of attack, decay, sustain, and release.

For developers, the API for the new QuickTime Music Synthesizer engine is unchanged from the existing API. The note allocator component is still used to access the synthesizer.

New Reverb to Improve Sound Quality

Along with a new synthesis engine, QuickTime 5 provides a new reverb algorithm that improves the quality of the sounds.

The polyphony available to the QuickTime Music Synthesizer is dependent on the type of computer it runs on. The CPU power of the computer is going to determine how much work the synthesizer can get done and that, in turn, will determine the polyphony.

Updated Music Control Panel

The Music control panel has been updated to automatically scan the QuickTime Extensions directory for either Sound Font 2 or DLS files. These appear in the list of “synthesizers” available to QuickTime, and the user can choose one of these sounds banks as the default bank to use to play back QuickTime Music content, if a specific sound has not been assigned in the movie.

Bear in mind that many QTMA movies assume a GeneralMIDI-compliant synthesizer, so generally a user should ensure that the default sample set is a GM-compliant sample set.

Other Improvements

There are a number of improvements to QTMA in this release. These include

• Export to AIFF now respects mono/stereo, bit depth, and sampling rate options, whereas previously these were ignored.

• Synth initialization has been much improved (custom sub-allocator).

• Playback of music movies should start soon after the user clicks Play.

• Improved Sound Font support, so that more files are now parsed correctly.

• MIDI Channel information is typically lost when importing and exporting MIDI files. This has been a longstanding issue with QTMA. This has now been addressed in this release.

Some Limitations of Sound Font 2 and DLS Files

Developers have been asking: How does QuickTime deal with large SF2 files? Does it load samples dynamically as they are needed by a MIDI track? What practical limits are there on SF2 size?

In response: Sound Font 2 and DLS samples are loaded only on an as-needed basis. There are practical limits on SF2 files, depending on how the file is laid out and how many of the samples in the file are used for a particular playback situation. Apart from memory availability, the size of the files (and even the size of the samples) are not an issue. If the memory is available, QTMA will use it.

There are some known limitations on both SF2 and DLS files, however.

1. Both formats have an internal name field for the entire sound bank. This should be set by the author of these files to be a meaningful name unique to that set.

QTMA uses this field as a way of identifying which sample bank is used if you assign an instrument to that bank. This is also the name that is used in the Instrument Picker dialog to allow users to assign parts (read MIDI Channels) of a music file to different sound banks.

1. Any use of the LSB as a way of selecting banks of sounds is not supported. This is only an option in DLS files. (SF2 files only supply the MSB for bank selects.)

For instance: (DLS only)

Bank-MSB Bank-LSB Patch Number

0 1 1

0 2 1

will result in the first patch being selected in both situations, as QTMA will only match on

Bank-MSB Patch Number

0 1

Assigning Custom Sound Banks to Movies

In general, music movies are made by importing a MIDI file into a QuickTime movie. During the import, no specific assignment of a part (or MIDI Channel) is assigned to an instrument. Thus, when a movie is played back, the default synthesizer that the user has selected in the QTMA Control Panel is used to render the parts of the movie.

Using QuickTime Player Pro, however, an author can assign particular synthesizers as well as different sound banks to a movie. To accomplish this, you follow these steps:

1. Open the Movie and choose “Get Movie Properties” from the “Movie” Menu.

2. When the dialog appears, choose the “Music Track” item in the top left pop-up menu.

3. In the top right pop-up menu, choose the “Instruments” item.

You now see a displayed all the parts found in this music track. Each part is signified by the name of the instrument used to render that part.

1. Double-click the instrument that you want to change. A dialog appears called the “Instrument Picker”, which shows you a list of the currently available sound banks and synthesizers.

2. You can choose a new sound bank with the top menu item. It will read “Default Synthesizer” initially.

Once you choose the sound bank you want to use for that part, you can choose the instrument from the sound bank you wish to use.

If you save the movie, the assigned sound bank is used during playback. Bear in mind that this sound bank will be searched for when you next open that movie, and should be present for the movie to be played back correctly.

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