Using Anedio D1 DAC with Logitech Squeezebox Touch
The home computer is increasingly becoming the hub of audio playback and storage. With the availability of large-capacity hard drives at affordable prices, the entire CD collection can be ripped and stored on a hard drive, and any song in the collection can be easily accessed through a media player with just a few clicks. The power and convenience of having all the music collection in one place is very appealing. In this rapidly-evolving era of computer audio, we at Anedio are continuing to experiment with various cost-effective solutions for high-performance digital playback.
For the computer-based audiophile system to be viable, we believe the following factors are important:
- Performance: We would like superior sonic performance that can make the Red Book CD sound better and reveal the sonic potential of the high-resolution 24-bit, 88.2K/96KHz format.
- Accessibility: We would like the digital archive of music to be easily accessible anywhere in the house.
- Cost: We are passionate about keeping the cost of the whole system reasonable so that more people can enjoy the highest quality music.
One obvious approach is to connect a computer to an external DAC through a USB or SPDIF cable, and use a media player program to send the audio stream. This direct approach works reliably; however, without a remote control, the computer may not be the most convenient device for playing music in a living room. Some audiophiles may object to the fan noise emitting from the computer and may want to place it in another room. Others may not want to have their computer tethered to their audio system through a USB or SPDIF cable.
Logitech Squeezebox Touch: Wireless Music Server
Another cost-effective approach is to use a wireless music server, such as the Logitech Squeezebox Touch, together with the Anedio D1 DAC. Priced at only $299, the Squeezebox Touch opens up a window of possibility for those searching for cost-effective, high-performance playback. It is quite flexible in the way it connects to various sources of digital music. It can stream music from a wireless network, Ethernet, or directly from a USB drive or SD card attached to it. Perhaps, the most interesting possibility for the greatest accessibility is the wireless.
Most importantly for audiophiles, it offers three indispensable capabilities:
- Bit Transparency: The Squeezebox Touch passes the audio data through transparently without modifying it in any way.
- High Resolution and Sample Rates: It supports 24-bit resolution and 88.2K/96KHz sample rates.
- Built-in FLAC Decoder: Its supported formats include FLAC, the most widely-accepted lossless compression format for high-performance audio.
These three features enable the Squeezebox Touch to be a high-fidelity digital transport, passing the audio data transparently to an external high-performance DAC.
In the wireless configuration, the Squeezebox Touch receives the digital audio stream from the wireless network already existing at home. The digital music files may be stored on a computer located in another room or on a network drive. The Squeezebox Touch serves as a wireless pass-through device that receives the digital audio stream and passes it on to an external DAC, as well as a music player that can be controlled via its touch screen or remote control. Even though its built-in DAC is good in their own right, especially considering the low price of such feature-rich equipment, its performance can be improved substantially by feeding the digital output to the D1 DAC through the SPDIF interface.
Measurements
Our tests confirmed that the wireless streaming through the Squeezebox Touch indeed preserved bit transparency for both 16 and 24 bits and for 44.1K, 88.2K, and 96KHz sample rates. All test signals were in the FLAC and WAV formats residing on a notebook computer. The process of wireless streaming through Squeezebox Touch is quite robust, as dropouts occur very rarely. We believe that the wireless connection is sufficiently reliable for high-performance home audio. In our test setup, the wireless router was about 30 feet away, with the signal strength in the Squeezebox diagnostics showing between 60% and 80%.
Shown in Fig. 4 is a jitter measurement of the Squeezebox Touch analog output with an 11.025KHz, 24-bit signal sampled at 44.1KHz. To expose as much frequency-coherent jitter as possible, we used very long FFTs, 1024K points, averaged 4 times. The multitude of small peaks that spread symmetrically around the signal are most likely caused by jitter. Most of the jitter-related peaks are within 1.1KHz from the signal frequency. Taking the RMS sum of the peaks between 50Hz and 1.1KHz from the signal, the jitter is estimated to be roughly 50 ps rms or 300 ps peak-to-peak.
It is surprising that this jitter pattern is consistent whether the data is streamed wireless or taken directly from an SD card or a USB drive. One might expect that jitter would be worse through wireless connection, but the fact that it is consistent regardless of the type of interface suggests that there is intelligent buffering taking place internally for the wireless stream.
When the same signal is fed into the D1 DAC, the whole FFT spectrum is cleaned up drastically, demonstrating the effectiveness of the multi-stage jitter reduction scheme for all types of digital input stream. The multitude of small peaks have completely disappeared; the only remaining jitter sidebands are below -150dB, +/- 1KHz from the signal. Also, the overall noise level is at least 20 dB lower, revealing the full capacity of high-resolution 24-bit music.
In sum, the combination of a wireless music server, such as the Logitech Squeezebox Touch, and the Anedio D1-DAC makes it possible to enjoy highest quality music anywhere in the house at a reasonable price. The bit-transparent wireless connection opens up the possibility of accessing the computer archive of music any place within the reach of the wireless network. The Anedio D1 DAC provides jitter-free conversion to the analog domain that will satisfy even the most discerning ears.