©2008 Logitech
Squeezebox Boom Audio Design
2
Although we believe Squeezebox Boom sounds great today, because of the extremely flexible
and upgradeable nature of the Squeezebox architecture, we can roll in new features on an
ongoing basis to meet our customers’ needs. Some of the future enhancements could include:
automatic loudness filter for low-volume listening; dynamic range compression for low-volume
listening; multi-band equalization; dynamic range compression for high-noise environments; and
whatever else we can think up to help improve the overall experience.
System Overview
The diagram below (Figure 1) shows a simplified block diagram of the Squeezebox Boom audio
system. For the purposes of this paper, we’ll break it down between CPU section and audio
section. The CPU section contains all the traditional Squeezebox components, such as the
CPU, Ethernet, display, IO, and user interface. This paper will not cover the Squeezebox CPU
and IO in any depth, but will be focused on the audio architecture and processing.
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Figure 1: Squeezebox Boom Block Diagram. This paper will discuss the audio design, starting at the I2S & I2C
interface between the CPU and Audio sections and follow the signal path through to the speakers, line-in and
subwoofer-out.
As seen in Figure 1, the audio section includes the primary digital audio processor chip (TI
TAS3204), the subwoofer/headphone DAC (Wolfson WM8501), the power amplifiers (TI
TPA3100D2 and TPA3101D2), and the loudspeakers themselves.
Digital Audio Processor
The TI TAS3204 digital audio processor is a high-performance DSP optimized for audio
applications, combined with high-performance (over 100 dB signal-to-noise ratio) DACs and
analog-to-digital converters (ADCs) built in. It also can send and receive multiple channels of
I2S to talk to secondary DACs or ADCs. The DSP processor itself is a 135 MHZ, 48-bit DSP,
with 28-bit coefficients and a 76-bit accumulator.
Secondary DAC
The secondary DAC, the Wolfson WM8501, is used to drive the subwoofer/headphone port. It
gets its digital signal from the TAS3204 via an I2S interface. The DSP software is configured to
process the signal differently depending on whether there is a subwoofer or a headphone
plugged in to the output jack. The user can select from the user interface the type of plug-in they
