WHIRLWIND QBOX-AES :
THE NEXT "GENERATION"
Several Qbox users and audio techs told us that they would like to be able to apply similar troubleshooting techniques to an AES digital audio system. A portable digital Qbox would allow a technician to verify that a sending unit is actually transmitting good data, whether or not received data contains usable audio or that a receiving unit is working properly. This led to the development of an AES version of the Qbox, the AESQbox.
The AESQbox generates AES-3 or S/PDIF digital audio from three analog sources: a built-in tone generator, a built-in condenser microphone or stereo line-in jack. It also receives AES-3 or S/PDIF digital and can output the analog audio via a line-out/headphone jack or its built-in speaker.
DIGITAL INPUT SECTION
AES digital audio is input to the unit via XLR or BNC jacks. It was decided that the AESQbox would recognize the most popular sample rates, ranging from 32 kHz to 192 kHz. A set of INPUT SAMPLE RATE indicator LEDs shows the following received sample frequencies (in kHz): 32, 44.1, 48, 88.2, 96, 176.4, and 192. The INPUT SAMPLE RATE LEDs have two presentations: steady ON indicates that the received signal has been transmitted in Professional Mode or slow flash (twice per second) indicates that the received signal has been transmitted in Consumer Mode.
A FAULT indicator flashes and a sample frequency indicator lights to show when a sample frequency is received, but the data is not PCM digital audio. When no sample frequency is received, all of the indicators are off.
If analog audio is present in the data, it may be monitored via a high quality unbalanced, 3.5mm TRS LINE OUT jack or with the built in speaker. There are separate LINE/PHONES and SPEAKER volume controls. The channel monitored by the speaker is selectable with a switch, CH A, CH B or BOTH. The output level obtained from the LINE OUT jack can be driven to greater than +4 dB, enough to drive pro-level equipment or stereo headphones.
A switch allows selection of MIC, AUX or TONE as the analog audio source. The built-in MIC is an electret condenser type and feeds both the left and right channels.
The built-in TONE generators provide 440 Hz tone for the left channel and 880 Hz tone for the right channel. The AUX IN is a 3.5mm stereo TRS unbalanced jack and accepts line level stereo audio. The level of all three sources to the output section is controlled by an OUTPUT LEVEL control. CLIP LEDs will start flickering at 3 dB below digital full-scale (DFS), and come on full brightness at 1 dB below DFS. Further increasing the level will result in a hard clip.
The analog signal is converted to AES digital and is output via the male XLR and BNC jacks. Output sample rates of 48 kHz, 96 kHz, or 192 kHz, may be selected with a three-position SAMPLE RATE switch. 1 However, when an AES digital stream is present at the digital input, the output sample rate will automatically duplicate the input sample rate, regardless of the SAMPLE RATE switch setting, causing a LOCKED TO INPUT indicator to illuminate.
Three operating behaviors are selectable with a MODE switch:
- IN/OUT: AES/EBU input and output sections operate separately except that as described above, the output sample rate will duplicate the input sample rate when an AES stream is applied to the input.
- PASS THRU: The digital audio received on the input is passed through to the output at the same sample rate so that the audio content may be monitored - the AESQbox is acting like both a "wiretap" and a "repeater". In this mode, the signal is passed from the input to the output while always remaining in the digital domain, thus preserving the original signal to the greatest extent possible.
- CABLE TEST: The analog source is encoded to AES and delivered to the AES output. You may then test your digital cable by connecting it from the output back to the AES input, which should allow the user to hear the tones, mic or external audio source. This verifies the integrity of the cable and doubles as a self-test for the unit itself.
One of the requirements of this design is that it is able to produce high quality audio. The AESQBox features high quality A/D and D/A converters and the line out has excellent THD and noise specs. This allows the AESQBox to double as a portable AES-to-Line or Line-to-AES converter.
Two AESQBoxes can be used as a hands free, two-way intercom. Set both units to the same sample rate then use two cables to connect the output of one to the input of the other, and vice versa. Set the analog source to MIC and put both units in CABLE TEST mode.
The dual digital XLR and BNC jacks use multiple secondary transformers allowing them to convert impedances from the AES standard 110 Ohms to the SPDIF standard 75 Ohms. The INPUT connector pair can perform one impedance translation, and the OUTPUT connector pair can perform another, even when the AESQBox is switched off.
Inputs and outputs are DC and transformer isolated to prevent inadvertent damage to the AESQBox.
The AESQbox is made in Rochester, NY USA and it's housed in a rugged metal case. The AESQBox operates on 4 AA size batteries or with the included AC power adapter. A POWER indicator shows that power is on and allows the user to assess battery condition - when it gets dim, time to change the batteries.