Idea&Principle

The Idea Behind TrueMatch

These were the reasons that made us develop TrueMatch. The objective was to achieve excellent THD&N values at high and low levels.
The idea is to run a standard 24-bit converter in its optimum operating range by deploying an adjustable preamp function; the converter must, however, never clip. TrueMatch achieves this by using multiple preamplifiers for various amplification ranges, each featuring its own A/D converter.
When a signal is applied, a processor selects the most suitable of the available converters on the basis of the signal level.
This so-called gain-ranging technique is well known; however, it has one shortcoming: All gain factors of the individual preamps and the errors of all converters must be known in order to compensate them. In particular it is the transition regions between any two converters that may cause difficulties.

The TrueMatch Logic

Stage Tec has invested many years of hard work into the development of a technique that not only converts audio signals but also permanently monitors all participating amplifiers and A/D converters: All relevant values are constantly being measured with extreme accuracy. Gain and offset errors, even phase shifts, and pulse-dependent distortion between the individual signal paths are recognized and immediately corrected. The corrections are much more exact than the A/D converters employed, meaning that correction errors are far below the converters’ noise floor and cannot be verified by measuring. For instance, phase shifts between the individual paths can now be corrected to a value better than 0.01° at 20 kHz.
Consequently, the corrections do eliminate not only component tolerances and aging inside the amplifiers used but also eliminate dispersion between the individual converters and parameter drifting caused by temperature changes. Thus, it is possible to use an A/D converter for calculating a signal that is being output by another converter — and even the noise floor of the other converter can be determined. Therefore these converters are »truly matched«.

The Implementation of the TrueMatch Converter

The preamp gain is stepped in such a way that exactly one A/D converter is operated in its optimum range just below its clipping threshold. Thus, to achieve optimum THD&N values over the entire dynamic range, the processor »simply« needs to find and select the A/D converter(s) with the most accurate conversion result and to calculate all necessary corrections. Therefore, it is practically possible to make converters with a resolution of more than 24 bits and a dynamic range of better than 144 dB. The 32-bit A/D converter manufactured by Stage Tec achieves a usable dynamic range of more than 150 dB.

The Analogue Side

Unprecedented demands are also placed on the analogue components. The amplifiers must be able to process voltage ranges of more than eight decades. They must work with both extremely low-noise and low-THD. Analogue and digital signals from converters currently not in use must not falsify the wanted signal by crosstalk.
Despite of the enormous effort needed, for example, by a fourfold-stacked 32-bit A/D converter, the Stage Tec converter requires even less supply power than the conventionally structured combination of microphone preamps and A/D converters.
TrueMatch has been patented in most countries and has also been licensed to other manufacturers. Stage Tec uses the system in all its high-quality converters, for example, for the XAD+ and XMIC+ boards.

Parameters

More than 45 correction parameters (some fixed, some variable) are determined individually for each converter stage inside Stage Tec‘s 28-bit converters. All these parameters are then considered during the conversion process.

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