Performing audio measurements on the FV-1
Although the FV-1 has excellent sound quality, certain precautions must be taken to properly characterize the distortion and noise qualities of the part. This is primarily due to the use of a 128X over sampled delta sigma DAC, which produces a small amount of out-of-band noise that although inaudible, must be removed when measurements are made with wide-band analysis equipment.
The problem is best overcome with a post filter that preserves the body of audio information, up to 1/2 the part's external clock frequency, rejecting all higher frequencies. Most distortion and noise measurement equipment have such filters available, but rarely are they effective enough, especially when using the more economical 32768 crystal, where the cutoff frequency is best placed at 15KHz.
A typical schematic for such a filter:
These values would be appropriate for a 32768 crystal, but should be scaled for high clock frequencies.
Be aware that the out-of-band noise from the FV-1 is extremely low, only adversely affecting precision measurements. When used to drive speaker systems, the out of band energy is so low that it would burden HF drivers by only a few milliwatts in a high power system.