Scientific background, analyses, syntheses & audio examples

Frequency Spectra of Virtual Trombones by several manufacturers

It has been suggested by some that Samplemodeling™ The Trombone may sound “thin”, lacking some low frequency content. In a forum, very little content below 300 Hz has been judged to be present in a bass trombone demo:

http://www.vi-control.net/forum/viewtopic.php?t=16602

To clarify the issue, we performed a comparative spectral analysis of several notes in the low range of the instrument of the renowned Advanced Orchestra, Vienna Symphonic Library and Samplemodeling Tenor Trombones, the latter without and with “early reflections” Impulse Response.

The analysis was carried out on a 2 sec sustain portion of forte samples, normalized to -9 dB.

Download the audio examples (each note is played, in sequence, with: Advanced Orchestra, Vienna Symphonic Library, Samplemodeling The Trombone anechoic, SM The Trombone with early reflections):

Due to normalization, and to the overall spectral shape of these samples, the energy of each triplet was approximately equal around 1 kHz. The three samples showed differences in the high frequency range, partly due to differences in the actually played dynamics. AO was generally brighter than SM and VSL.

In the low frequency range, AO and VSL were affected by some discontinuities in the energy of the lower harmonics, most likely due to ambience-related phase cancellations. SM samples (recorded in an anechoic chamber) were free of these artifacts. Moreover, SM samples always showed greater (up to 15 dB) energy content below 300 Hz than either VSL or AO. A comparative spectral analysis on Samplemodeling Tenor Trombone with and without early reflections showed basically identical results. Only the anechoic sound was therefore shown in the graphs.

Conclusions:

• Conventional (ambience) recording may lead to spectral inhomogeneities, due to phase cancellations.
• Anechoic recording yields a homogeneous spectrum, with no phase cancellations.
• The Tenor Trombone of Samplemodeling has higher energy content in the low frequency range than either Advanced Orchestra or Vienna Symphonic Library.

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SM Bass versus Tenor Trombone

To verify whether the Bass Trombone had lower energy in the low frequency range than the Tenor Trombone, a comparative spectral analysis has been carried out on the E1 samples of each instrument.

Conclusions:

The Bass Trombone exhibits greater energy than the Tenor Trombone (up to 6 dB) in the low frequency range.

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The overall spectrum of Samplemodeling Bass Trombone, and its dependency on the dynamics

We performed a spectral analysis on a chromatic series of notes spanning over the two lower octaves (A#-1 – A#1), played with the Bass Trombone at various dynamics (CC11 = 20, 40, 60, 80,100, 120). The graph below only shows the spectra corresponding to the four lower dynamics, for the sake of clarity.

Conclusions:

below 400 hz, the spectral energy is basically equal at any dynamics, well represented down to 40 Hz.

above 400 Hz, the spectral energy progressively increases along with the dynamics, with a central peak sliding from 400 Hz (pp) to 800 Hz (f)