After more than a decade of exhaustive research we arrived at the conclusion that digital audio interfaces with higher bandwidth cause more degrading (more analytical, less realistic and less involving sound).
The reason for this is that higher frequencies can spread much easier to other circuits (unwanted cosstalk) through parasitic capacitances and wireless transmission. This way all DAC circuits will be affected and sound will be degraded.
These higher frequencies are outside the audio spectrum but will be demodulated by DAC circuits (similar to a radio receiver) and will then fall within the audio spectrum and become audible as degrading.
Because these demodulated interference signals now fall within the audio spectrum, these will pass the brickwall filter that is installed on most DACs.
This issue is the main reason for audible differences between different bit-perfect sources and interlinks that should -theoretically- all sound identical.
Following digital audio interfaces generate and use -very- large bandwidth = maximal degrading through crosstalk:
– USB
– S/PDIF RCA
– HDMI
– I2S and similar serial interfaces inside the DAC
– I2S external interface (usually using HDMI connectors and interlinks).
Often multiple digital audio interfaces (inputs) are integrated in a DAC to offer maximum flexibility.
This however will create even more degrading as each input circuit -adds- more unwanted high frequency interference and crosstalk even when not used / not connected.
Similar, higher sample rates = higher data and clock rates = higher frequencies = more degrading through crosstalk.
Other major problem is caused by ground loops —> noise injection in DAC circuits and all connected interlinks to audio equipment.
This problem is fully fixed by Toslink and similar optical digital audio interfaces.
S/PDIF RCA often has insulation transformers installed in an attempt to isolate circuits and prevent ground loops. But transformers are never perfect and will pass mainly higher frequency noise (input to output stray capacitance).
USB insulator chips have similar input to output coupling capacitance that passes high frequency noise and its circuits add more noise and jitter.
Optical USB adapters with external power supply have the receiver (that generates very high frequency interference) connected directly to the DAC injecting noise and creating a ground loop.
I2S external interfaces usually offer no galvanic insulation and the interlinks introduce extra jitter. Isolated external I2S interfaces will add jitter / pass high frequency interference
So a single Toslink DAC input offers 3 major advantages over all other digital audio interfaces:
– Low bandwidth = minimum crosstalk in the DAC circuits and connected equipment.
– Perfect galvanic insulation with zero input to output stray capacitance —> zero ground loop noise injection.
– Minimal noise injection into the DAC circuits as there is only one single input generating noise.
It is certainly true that Toslink introduces jitter (spectrum) issues with mainstream DACs. compared to some alternative digital audio interfaces like S/PDIF coax.
This is mainly caused by jitter and reflections caused by the optical interface in combination with mainstream S/PDIF receivers that are based on clock recovery (clock is extracted from Toslink, not generated from a low jitter masterclock).
The mainstream S/PDIF receivers will always fail to block all Toslink jitter regardless of S/PDIF receiver chip (crystals won’t help either and are only added for more stable traking at highest sample rates).
There are few if any effective S/PDIF reclocker / re-timing circuits, so the end result is a jitter problem with Toslink as is generally accepted.
So in most cases other interfaces that offer lower jitter are used instead and labelled “audiophile” despite related high frequency related noise injection and analytical sound.
DSP or tube output stages are often used in an attempt to mask this analytical sound, adding more distortion and degrading to the signal.
DSP applied on already mastered digital audio files will always add more degrading. The original, native hi-res studio recording (that won’t be offered) is required for maintaining lowest degrading when applying DSP.
—> Our PowerDAC series are fundamentally different from all mainstream DACs.
Incoming Toslink signal (low bandwidth) is sampled by a discrete custom DAPI (Digital Audio Parallel Interface) receiver. It scrapes only data from Toslink and -does not recover any clocks- for sample timing.
Audio data is first stored in a buffer memory. Next it is output in -parallel- (up to 48 separate I/O lines). The single timing sample signal is divided down from a completely independent, local low jitter masterclock.
So we have parallel data (up to 48 I/O lines) and a latch pulse signal that is divided down from the masterclock and has minimal energy (minimal energy = minimal power = minimal unwanted crosstalk).
We do not generate nor use any conventional I2S or similar serial interface signals in our PowerDACs, so related crosstalk issues are completely eliminated.
We now have:
– Single Toslink input with low bandwidth and minimal crosstalk inside the DAC.
– Complete elimination of ground loops and ground loop noise injection.
– Perfect sample timing (very low jitter, independent from the source & optical interlink jitter) provided by an independent, local, low jitter master clock..
– Lowest practical frequencies inside the DAC by DAPI, lowest practical crosstalk inside the DAC, involving and realistic sound (not analytical).
Because of this unique custom DAPI receiver we achieved highest practical source & interlink immunity.
I hope this clears things up about why we only installed one single Toslink input.
We also developed the ElectroTOS interface, this is a Coaxial / Toslink hybrid interface that combines advantages of coax (low jitter compared to optical interlinks) with short optical path (Toslink providing perfect galvanic insulation):
ElectroTos
The improved signal quality can be seen on the measurements and is comparable with S/PDIF coax. ElectroTOS can be used with all DACs that have standard Toslink input.
It is generated by our UT96 and UT192 USB reciever modules.
Existing digital audio sources can be easily modified to output a ElectroTOS compatible 3.3V signal (existing RCA coax outputs have too low voltage for the LED that requires 1.8V and won’t work).
All our PowerDACs can be easily connected to audio sources with a Toslink interlink.
