A specification-compliance test for SoundFont synthesizers.
Updated 9/8/24 by S. Christian Collins
The following tests will check to see if your SoundFont player is compatible with the SoundFont 2.01 and/or 2.04 specification, using the hardware implementation found in the Sound Blaster Audigy 2 ZS as a reference point. This test will not cover every possible implementation flaw, but should give a decent overview of a SoundFont player's compatibility with the specification.
To run the test, load the accompanying SoundFont bank into your SoundFont synth as bank 0, and then play the MIDI file. Use Audigy2 ZS, custom fx.ogg in the recordings folder as a reference for how these tests should sound. Note that for some tests, FluidSynth provides a more ideal rendering, especially when it comes to the filter behavior.
This test uses all six envelope stages, each lasting exactly 1 second. The stages are delay, attack, hold, decay, sustain, and release. The attack should be a convex curve, while the remaining envelope stages should all be linear. Note that viewing these stages on a waveform view in dB, the attack will appear linear, and the other phases will appear concave. The test starts with a click. You should hear the note's volume change according to the following envelope shape:
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This test uses all six envelope stages, each lasting exactly 1 second. The stages are delay, attack, hold, decay, sustain, and release. The attack should be a convex curve, while the remaining envelope stages should all be linear. You should hear the note's pitch change according to the following envelope shape:
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You should hear five tones at the same pitch, each one increasing in duration of the decay phase.
You should hear five tones at the same pitch, each one increasing in duration of the hold phase.
You should hear the volume oscillating at a moderate speed (4 Hz). The LFO depth value is set to 6 dB, which means the sample volume should oscillate between +6 dB and -6 dB.
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Test A: Velocity = 127. Since there is no attenuation to the sound at instrument or preset level, the sound cannot be amplified. Therefore, the LFO will only cause a reduction in volume, but never a boost. In a waveform view, the volume peaks will appear to be "chopped off". See the notes for test 12 below.
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Test B: Velocity = 90. Since there is attenuation to the sound due to the lower note velocity, the LFO can both amplify and attenuate the sound. In a waveform view, the volume oscillation should appear as a triangle wave.
You should hear the pitch oscillating at a moderate speed (4 Hz).
Which LFO is activated via mod wheel? It should be the vib. LFO. In this test, if the vib LFO is properly being activated, there should be a mild vibrato (4 Hz). However, if it is activating the modulation LFO instead, then the vibrato will be very fast.
You should hear three tones, all at the same pitch.
You should hear a white noise wave filtered using a low-pass filter at each of the following values:
| Cutoff frequency (Hz) |
|---|
| 20 |
| 50 |
| 100 |
| 200 |
| 500 |
| 1,000 |
| 1,500 |
| 2,000 |
| 3,000 |
| 4,000 |
| 5,000 |
| 6,000 |
| 7,000 |
| 8,000 |
| 9,000 |
| 10,000 |
| 12,000 |
| 15,000 |
| 17,500 |
| 20,000 |
Note that Sound Blaster hardware has an unusual filter that is fully open at 8,000 Hz. FluidSynth implements a proper 2-pole lowpass filter. See my video here on this topic.
You should hear a white noise wave filtered using a low-pass filter at 4,000 Hz while increasing the filter resonance (Q) using the following values:
| Filter Q (dB) |
|---|
| 0 |
| 5 |
| 10 |
| 15 |
| 20 |
| 25 |
| 30 |
| 35 |
| 40 |
| 50 |
| 70 |
| 96 |
The Sound Blaster hardware filter resonance appears to be capped to a maximum of 20 dB.
Each 1 dB of attenuation set at the instrument or preset level should only attenuate the sound by 0.4 dB. This is a quirk of the Sound Blaster hardware that should be emulated for compatibility with existing SoundFonts. Recent versions of Polyphone translate this value in the editor so you can see the actual attenuation amount.
For this test, you will hear a series of tones getting progressively quieter, based on the table below:
| dB in SoundFont | actual dB attenuated |
|---|---|
| 0 | 0 |
| 5 | 2 |
| 10 | 4 |
| 15 | 6 |
| 20 | 8 |
| 25 | 10 |
| 30 | 12 |
When measured, the volume decrease between each tone should be exactly 2 dB.
The same test as #11 is repeated, but with preset attenuation set to -12 dB. All tones should play at the same volume.
On Sound Blaster hardware, a playing sample (or "voice") can either be at full volume (0 dB) or attenuated below that level. No modulator, LFO or attenuation parameter value can raise the sample playback volume above this 0 dB limit. It is possible to set negative attenuation values at the preset level. However, if a voice has not been attenuated by a modulator (e.g., velocity, CC7, CC11), envelope, or by the attenuation value at the instrument level, then it cannot be boosted. In other words, a negative attenuation value in the preset can only boost the voice volume up to 0 dB, but never beyond.
Measured at the following velocities: 127, 111, 95, 79, 63, 47, 31, 15.
- Test A: default (should be 96 dB concave. The difference between 127 & 111 should be 2.34 dB)
- Test B: 144 dB concave
- Test C: 48 dB concave
- Test D: 96 dB linear
- Test E: modulator deleted from the instrument (all tones should be the same volume)
All tones should be the same volume, assuming test #13 is passed. Measured at the following velocities: 127, 111, 95, 79, 63, 47, 31, 15, with filter cutoff set to 4,000 Hz, and filter resonance at 10 dB.
The result of this test will vary depending on which spec version is implemented by the SoundFont synth:
- 2.01 spec: should perceive moderate filtering (-2400 cent curve) as the velocity decreases, with a distinct jump when passing over velocity=64 (due to the secondary modulator source=switch).
- 2.04 spec: should perceive moderate filtering (-2400 cent curve) as the velocity decreases
- Earlier spec versions: no filtering should occur
Because of this inconsistent behavior and the different way each version of this modulator must be canceled/overridden by the SoundFont designer, many SoundFont synths including FluidSynth and BASSMIDI choose not to implement this default modulator.
The result should be a smooth progression over a wide frequency range for the low pass filter, with noticeably more filtering at low velocities than the default velocity-to-FC modulator.
On the Sound Blaster Live!, instruments with attack 6 ms or greater enable filtering at lower velocities. This test attempts to see if this behavior is emulated. If Test A does not result in a filtered sound but Test C does, then this old behavior is emulated. If Test A sounds filtered, then ignore the results of this test.
Tests to see if the synth responds to the 2.01 spec method of canceling the default velocity-to-FC modulator. If so, all tones should have the same filtering. Ignore this test if the default modulator is not implemented (see Test A).
Tests to see if the synth responds to the 2.04 spec method of canceling the default velocity-to-FC modulator. If so, all tones should have the same filtering. Ignore this test if the default modulator is not implemented (see Test A).
You should hear a smooth opening and closing of the filter, which is being controlled by the mod wheel (CC1). If this isn't implemented, you will probably hear vibrato instead.
You will hear either "supported" or "not supported".
- Test A: Instrument-level reverb = 0%, 33.3%, 66.6% and 100%.
- Test B: MIDI CC 91 reverb = 0% (0), 33.3% (42), 66.6% (85) and 100% (127).
- Test C: Both instrument-level and MIDI CC91 reverb = 0%, 33.3%, 66.6% and 100%.
- Test A: Instrument-level chorus = 0%, 33.3%, 66.6% and 100%.
- Test B: MIDI CC 93 chorus = 0% (0), 33.3% (42), 66.6% (85) and 100% (127).
- Test C: Both instrument-level and MIDI CC93 chorus = 0%, 33.3%, 66.6% and 100%.
This test must be performed by ear. If the sound is grainy, a low quality interpolation method (e.g., "linear") is probably being used.
- Test A: Default (+/- 2 semitones) --you will hear middle C bend down a whole step and back, then up a whole step and back.
- Test B: Modulator removed (should hear no pitch change)
- Test C: Inverted --you will hear middle C bend up a whole step and back, then down a whole step and back.
Very short noise = exclusive class is supported Long noise = exclusive class is not supported