Sound Quality Factor (SQF)
What is It?
Many folks talk about the sound quality of various sound decoders in very subjective ways. Bruce wasn't satisfied with this. While the final quality of the sound is VERY dependent on the speaker system design, the better the sound quality from the decoder, the better the overall installation will sound.
The number of bits is important. But it doesn't tell the whole story.
The sampling rate is part of the mix, too. But by itself, it doesn't do the trick.
While driving back to Munds Park from the Tehachapi Loop, Bruce got the idea of a Sound Quality Factor rating for decoders. He will be providing the rating for all sound decoders we sell as he can acquire the data. This SQF number is a relative rating of the sound quality that the decoder is capable of producing. This is the ability of the hardware to reproduce sound programmed into the decoder.
It does NOT comment on the quality of the basic recording.
It does NOT take into account amplifier power or the speaker system being driven.
SQF is a calculation, based on the number of bits of sound data and the sampling rate in KHz. What is really important is the relative values for different decoders. Use this as a yardstick.
The bigger the number, the higher the ability to reproduce sound quality.
The table below shows popular sound decoders and compares SQF for each. Since the highest frequency a digital system can reproduce is half of the sampling rate, that number is included, too. Bruce believes that 8 KHz is the minimum high frequency for decoders to provide good bell and whistle (horn) tone and he personally prefers 12 KHz. Human hearing extends as high as 15 to 20 KHz.
| Mfr | Decoder Series | MSRP US$ | Bits | Sample Rate KHz |
Highest Frequency | SQF |
|---|---|---|---|---|---|---|
| Digitrax | SoundFX | $80 | 8 | 11 | 5.5 KHz | 88 |
| ESU | LokSound V3.5 | $139 | 8 | 12 | 6 KHz | 96 |
| ESU | LokSound Micro | $139 | 8 | 12 | 6 KHz | 96 |
| ESU | LokSound XL | $239 | 8 | 12 | 6 KHz | 96 |
| SoundTraxx | DSD-101LC | $65 | 8 | 24 | 12 KHz | 192 |
| SoundTraxx | DSD-100LC | $70 | 8 | 24 | 12 KHz | 192 |
| SoundTraxx | DSD-090LC | $80 | 8 | 24 | 12 KHZ | 192 |
| SoundTraxx | DSX | $85 | 8 | 24 | 12 KHz | 192 |
| SoundTraxx | Tsunami Series | $119 | 16 | 44 | 22 KHz | 704 |
Photo Above: BNSF Coal Drag, Palmer Lake, CO, © 2004 Michael W. Blevins