While developing the new SFZ percussion library for MuseScore, I have run across a number of shortcomings in Zerberus that we will need to fix before we can release this library. Everything mentioned in this report can be tested using the attached project file. Instructions:

1. Download the attached test file.
2. Copy the .sfz file and sample folder to MuseScore's SoundFont directory.
3. Load the test .mscz file into MuseScore.
4. Go to "View" -> "Synthesizer" and click "Load from Score" to load the samples.
5. Play the project. WARNING! The third test can get quite loud, so be ready to turn down the volume.

Here is what needs to be addressed:

Add Support for the Following Opcodes

delay= [0 to 100 seconds]

Description: Region delay time, in seconds. If a delay value is specified, the region playback will be postponed for the specified time. If the region receives a note-off message before delay time, the region won't play, unless the loop mode for the region is set to "one_shot". All envelope generators delay stage will start counting after region delay time.

Comments: This opcode is necessary to create a realistic ensemble effect out of solo samples.

pan= [-100 to 100]

Description: The panoramic position for the region, in percent. If a mono sample is used, pan value defines the position in the stereo image where the sample will be placed. When a stereo sample is used, the pan value defines the relative amplitude of one channel in respect to the other. A value of zero means centered, negative values move the panoramic to the left, positive to the right.

Comments: Stereo positioning is necessary for even the most basic sound design. I was surprised that Zerberus doesn't support this. In addition to "pan", the "width" and "position" opcodes should ideally be supported as well. More info regarding SFZ stereo positioning can be found here: http://www.drealm.info/sfz/plj-sfz.xhtml#stereo

offset= [0 to 4294967296]

Description: The offset used to play the sample, in sample units. The player will reproduce samples starting with the very first sample in the file, unless "offset" is specified. It will start playing the file at the "offset" sample in this case.

Comments: This opcode is needed for simulating release samples and section rolls.

group_volume= [-144 to 6 dB]

Description: The volume for the group, in dB.

Comments: This opcode is unique to the ARIA engine, but in my opinion should be implemented by other SFZ players as well. The "group_volume" opcode will adjust the volume of an entire group at once, which is especially useful in cases where the "volume" opcode is being used to adjust individual sample balance within the group. Here is a brief example to show why "group_volume" is desirable:

Observe the following SFZ code:

<group>
<region> sample=1.wav
<region> sample=2.wav
<region> sample=3.wav volume=-2
<region> sample=4.wav

You can see that sample "3.wav" has been attenuated by 2 dB. Now, let's say that I later determine that the entire group is too loud and I want to reduce the entire group -6 dB in volume. If I add the opcode "volume=-6" to , the actual result would be that samples 1,2 and 4 would now be playing at -6 dB, but sample 3 would still be playing at -2 dB, making it now louder than the rest of the group. I would have to manually change sample 3 to "volume=-8" to keep it 2 dB quieter than the rest of the group. In this example, such an adjustment is trivial, but in more complex groups, it can be a lot of work, especially if the SFZ author has to test different group attenuation values to find the right one.

This is why the "group_volume" opcode exists. If I use "group_volume=-6" in instead, then every sample is adjusted down 6 dB from where it is individually set to be. So, in this example, samples 1,2 and 4 would now be playing at -6 dB and sample 3 would be playing at -8 dB.

filters (fil_type=, cutoff=, etc.)

It appears that filters are currently not implemented at all in Zerberus. Adding support for filters (lowpass, highpass, 1 pole, 2 pole, etc.), filter envelopes and velocity tracking would be a nice addition that would allow us to create more realistic changes in an instrument's tone as the dynamic level changes. Without support for filters, quiet drum hits will sound identical to the loud hits, just quieter.

Bugs

For the bugs, I have created individual bug reports, linked here:
1. Bug #271719: zerberus: repeated release samples play louder and louder until everything is a distorted mess. If a "trigger=release" region is still playing when a second instance of the same region is triggered, the second instance will play louder than the first. If further instances continue to be triggered in a similar manner, subsequent samples will play progressively louder until you are left with a distorted mess.
2. Bug #271722: zerberus: long release samples do not play in their entirety. Release samples only play for about 3 seconds then quit.
3. Bug #271718: zerberus: frequent clicking noises when playing samples.