Sound Devices receives numerous inquiries regarding specifics of the 7-Series recorders. Here are a few of the most popular questions. Note that this FAQ is frequently updated as features and specifications are subject to change.

Is there any way to upgrade a 702 to a 702T, or a 702 to a 722, or a 702T to a 744T?

No. While quite a bit of the electronics are shared, many of the features, specifically data storage, time code, and I/O are unique to each product. Please consider your needs carefully before purchasing since each product is unique.

Microphone Preamplifiers:

How good are the microphone preamps?

The preamps on all 7-series recordersare superb and unique. We took advantage of the increased power available from Li-ion batteries and developed a preamp that is quieter, exhibits lower distortion, and has far higher bandwidth than any other [present] Sound Devices preamp. They use a large geometry, discrete transistor topology versus the transformer preamps of our field mixers. While bandwidth out to the Nyquist frequency at 192 kHz sampling rate may not be needed for music recording, it is important for scientific test and measurement applications.

How do they compare to other high-end portable preamps and recorders?

You can favorably compare our new preamps to any other recorder, stand-alone mixer, or dedicated preamp. While our field mixers are renowned for their performance, the 7-Series goes beyond them. The listeners ears and tastes are, of course, the ultimate judge.

What are the pros and cons of your transformer-less preamp design?

Way back in 1998, when developing our first product the MP-1, we built a number of prototypes with different transformer combinations with the typical premium transformer brands. Matt Anderson, our chief engineer, had designed a few mic-level transformers in an earlier life, so he was particularly critical of their construction and electrical performance. Matt used a Lundahl part in our first product’s circuit because of its excellent handling of high signal levels, low distortion–particularly at low frequencies, and wide dynamic range. It also is a good part mechanically and its footprint is convenient on a circuit board. That original MP-1 preamp is the basic core of preamp design in the MM-1, MP-2 (discontinued), MixPre, 302, and 442. You can bet that we will use it again in later field mixer designs.

Quality mic-level audio transformers have excellent common-mode rejection, galvanic isolation, plus passive gain. That last point is quite useful in a field mixer powered by a few penlight batteries. Transformers are a benefit in the field, especially with unknown audio sources. In addition, they have their own sonic characteristics by being somewhat non-linear. Their downside is that they are physically large, heavy, and expensive.

Enter the 7-Series recorder…

To keep size and weight of the recorders down, and since we have the luxury of (relatively) ample current via our Li-Ion battery, we pursued designing a circuit which equals a transformer all the way around. This unique input stage is a classic long-tailed pair (using some very low noise discrete transistors) with some unique twists. Very high common mode impedance is achieved, which yields excellent common mode rejection. One of the most wonderful aspects of a well designed transformer stage is low noise at low gains. Most transformerless input stages (SSM2017, INA163, etc) do have excellent noise performance – with the input trim cranked to 60 dB of gain. This new circuit has very low noise across the gain range, an extremely low THD (0.004%) and has excellent noise cancelling characteristics. We feel that it rivals or betters any mic pre on the market sonically, transformer or transformerless.

Do the mic preamps have T-power?

T-powering is not included on the 7-Series recorders. If T-powering is required, we recommend using our 442, 302, or MM-1 as the front end to the recorder.

Powering:

How is the battery life?

Runtime tests vary depending on numerous factors,, but fully loaded usage at the highest bit rate with two inputs, outputting time code, writing to a 5400 rpm HD is less than 1 A (@ 7.2 V). This means that an XL-B2 battery (4500 mAh provided with the 722 and 744T, XL-B1 @ 1800 mAH provided with the 702 and 702T) battery can deliver at least 3 hours and the larger 6000+ mAh Sony batteries will perform quite well. Don’t forget that the unit can easily be powered by typical bag power solutions.

The removable battery is a 7.2 V Lithium Ion rechargeable cell; external DC accepts 10-18 VDC. Current draw on the external DC will be higher if the on-board cell needs to be charged. The 7-Series operates just like most notebook computers—if external power is applied, it will run the unit and charge the removable cell (if needed).

Just like our mixers, there is no performance benefit from powering from higher or lower voltages. As long as the external power supply or removable battery provides the necessary voltage and current, the unit’s switching power supply will generate the needed voltage rails for operation. The 7-Series can accept external voltages from 10-18 V (different than our mixers, which can accept voltages down to 5 V).

Can the meters be turned off to be less intrusive and less power hungry?

Yes, and to save your corneas. Brightness is fully variable; control is adjusted with the rotary encoder, just like a light dimmer. There is also something we call “stealth mode” which turns all LED’s and backlighting off. The back light display (and buttons) can be on or off.

If trying to conserve power, what works best?

Lowest power draw would be no phantom, no timecode output, display brightness all the way down, lower sample rates, and writing to Compact Flash only (the internal hard drive will spin down on the 722 and 744T). If you need to be ultra-current conscious with the 722 and 744T, pull the hard drive. On power up the drive always spins up for verification. If you pull it, you eliminate any power draw from the drive.

What happens if I yank the battery off the unit while I am recording?

The unit will turn off. We have just enough capacitance in the unit to close the file being recorded, but it is not recommended to remove the battery during media formatting or recording. If you do need to swap batteries WHILE recording, you will need an external DC supply connected to make the change. Our battery charging implementation is just like most notebook computers, which charge the on-board battery from external DC.

Storage Medium – Hard Drives or Compact Flash:

Is there anything to watch out for when substituting high capacity (100+ GB) hard drives in the 722 and 744T?

Storage capacity isn’t as much of an issue as is drive current draw. For instance, 7200 rpm drives draw more current and generate more heat than 5400 and 4200 rpm mechanisms. Higher speed drives will have less runtime than lower speed drives. In general, the heat generated from the drive will be in the same range regardless of its size and capacity. We have tested drives up to 250 GB (the largest available 2.5-inch notebook drive as of March ’07) with good success.

Are the 722 and 744T hard drives removable / replaceable?

While drives in these units are replaceable, internal hard drives are not intended to be used as a swappable medium. The hard drive is installed inside the unit and requires screwdriver access. The drive is “suspended” in the unit with an isolating membrane and is attached to the circuit board via a flex circuit board. One would typically replace a drive to change capacity or hard drive type. Transferring audio data via FireWire or using CompactFlash is far quicker and easier. Drive replacement has no warranty implications.

Can the 702 and 702T accept hard drive ?

These units are CompactFlash card only. The circuitry for them to accept a hard drive is absent. You can, however, record to a FireWire-connected external hard drive. There is no upgrade path to an internal hard drive with the 702 and 702T.

How do you format new recording media (hard drive and/or CompactFlash)?

When an unformatted hard drive, CF, or external FireWire drive is connected to the recorder the user is prompted to format media if it is not already a FAT32 volume. If a new volume has audio or other data files present but the medium is not a FAT32 volume, the 7-Series will see the volume as unformatted and prompt for formatting. This will erase any and all data files on the drive. A volume already formatted as FAT32 installed into the machine will be ready to record immediately. Formatting takes roughly 10 seconds (equivalent to a “fast format”) for a hard drive and will vary based on the speed and size of the volume.

A useful utility on the recorder is its “media speed test.” A newly installed hard drive or CompactFlash can be speed tested to measure its record throughput. This is especially useful with CompactFlash, since the rated speed of CompactFlash is often quite different than its actual throughput.

What about 722 and 744T hard drive performance with shock and vibration?

Sound Devices has spent quite a lot of investigation qualifying hard drive shock and vibration performance. Our big green shaking machine (one of several environmental test tools purchased from the former Jensen loudspeaker laboratory in Schiller Park, IL) has been hard at work testing drives and units. Drive vendor datasheet information does not correspond to the realities of the physical world and to the specific buffering and caching scheme we use. Sound Devices will provide the drive with the most shock and vibration immunity for our implementation. Either a 4200, 5400, or 7200 rpm 2.5-inch mechanism will be supplied. Our interface supplies both 5 V and 3.3 V rails to accommodate 2.5-inch or 1.8-inch drives.

Do note that with ANY hard disk recorder or player, if the drive is subject to severe impact it can fail. If severe service condtions are anticipated, recording to solid state (CF) media is recommended.

I’d like to find out about the acoustic noise that the 7-series make. Is the unit quiet enough to be in the same room as a quiet audio source?

In our testing, hard drive noise is nearly imperceptible on the 722 and 744T unless one actually presses their ear against the unit. The 702 and 702T generate no acoustical noise since they are completely solid-state units. It is safe to say that the unit can be in immediate proximity of very quiet sound sources while recording to the internal hard drive. You may hear a faint noise when the drive first spins up (powering up or when the unit goes into record following a long period of inactivity), but during continuous read/write, it is certainly quieter than a DAT transport.

Do note that when hard drives in the 722 and 744T begin to fail their bearings begin to get quite loud. In that case it would be impractical to record to the internal hard drive. It would then be time for a drive replacement.

Will any hard drive support the maximum number of channels at the highest bit depth and sampling rates (24-bit/192 kHz)?

Certainly. The throughput on 5400 rpm and higher hard drives supports the maximum record rates of the devices. The benefit of higher rpm drives is during transfer. There is a few percent increase in transfer speed stepping from one drive speed to the next.

What about CompactFlash with high sampling rates?
While we allow writing 192 kHz sample rate files with CompactFlash, some slower CF cards may have throughput problems and have media errors. The user will be notified with a warning tone in headphones and a front-panel indication that a write error has occurred. Our on-board CF speed tester is a good tool to determine if writing to 192 kHz is possible with the installed CF card.

How do you handle the 2 GB file size limit that is often associated with .wav files? Will the file system break a recording seamlessly at a given file size and start a new one without any operator intervention?

There are couple of things here. First, a WAV file on its own isn’t technically limited to 2 GB. Some early audio software applications use signed numbers instead of unsigned numbers for their file pointers. This caused an artificial 2 GB limit. With our recorders, it is the volume that contains the WAV which limits its size. In older FAT (and FAT16) environments the largest single volume (and file) was 2 GB (remember the fun when installing a large drive with Window 95 and having multiple partitions?).

The 744T and 722 recorders data volumes are formatted and write to FAT32 file structures. This formatting allows the drive to directly mount in a wide variety of computer platforms, including Windows, Mac OS, and Linux. Via the FireWire connection both internal drives (internal HD and CF) appear as external FAT32 volumes. The 7-Series recorders can format volumes up to the 2 TB. (NOTE: Windows XP has a limitation on FAT32 drive formatting – XP can format a FAT32 volume to a maximum of 32 GB, although it can read FAT32 volumes as large as 2 TB.)

FAT32 formatting has a maximum single file size limitation of 4 GB. While that means that you could have thousands of files on the drive, the largest any one file can be is 4 GB. The 744T and 722 recorders will automatically split an audio file before the 4 GB size is reached and begin writing to a new file. When joined in an editing program these files match seamlessly with no samples lost. This is similar to an Audio CD which has multiple tracks on its volume. The 744T and 722 have menu-selectable file size maximums of 650 MB, 1 GB, 2 GB, and 4 GB. The 650 MB size allows the user to break a single, long form audio program into multiple CD-R sized files for backup to inexpensive CD-R medium.

Recorder Control:

Does the unit indicate time remaining or capacity of either hard drive or CompactFlash?
Based on three factors: record sample rate, bit depth, and number of recording tracks enabled, the front panel will indicate time remaining on the selected recording medium, either HD or CF.

What happens when “REC” is pressed while recording?
Depending on what is selected in the user menu, pressing REC during recording will either place a marker within the recorded file, or “split” the file and begin a new one (see file break above). Note that you can select whether pre-roll buffers apply to split files.

Gain Control:

How are the input levels controlled?

702, 702T, 722 – when its inputs are in mic-level, the front panel level controls adjust the analog preamp trim level and are continuous analog trim controls. In line position they act as stepped attenuation controls.

744T – inputs 1 & 2 as above, inputs 3 & 4 are menu adjustable for attenuation level similar to line inputs 1 & 2.

For both units, there is digital attenuation at the AES3id outputs, no digital attenuation at the input.

I have a Soundfield microphone. Can I control the levels of all line-level analog inputs accurately?

With Soundfield microphones, you use the 744T to record the four-track raw B-format audio from each discrete capsule. When inputting at line-level, each input can be adjusted in 0.1 dB increments for precise matching of each input.

Channel Routing:

When recording 4-channels to the 744T, can any input be assigned to any track?

Yes. This is a very important function and the input routing is indicated by 16 front-panel blue GaN LED’s. Any input can be assigned to any record track. The user menu is easy and fast to route inputs to tracks.

When playing back a four channel recording from the 744T how do you route to the two analog outputs or is there a provision for mixing all channels to outputs?
Two, two-channel output buses are present on the 744T – bus 1 and bus 2. Bus 1 has both analog and digital outputs and bus 2 is digital output only. The routing of inputs and tracks to these buses is assignable in the user menu. Assignments include:

What is “input delay” and how much is available?

There is selectable microsecond delay for each of the four inputs, (not tracks). This delay can be applied to “time align” audio sources arriving at the inputs. For instance, all A/D converters have a measurable delay from their analog input to their digital output. This group delay, or latency, can be accounted for at the inputs of the 744T. Analog inputs can be delayed to match the delay from the external A/D converter. This offset will be recorded, so it may prove to be a source of user-induced error if someone applies it incorrectly.

Can the input delay be changed after recording?

Delay is printed to the file, however, most multitrack DAW’s (Digital Audio Workstations) allow slipping tracks. You would want to know what delay was applied in order to accurately undo it, unless there is some sort of slate to align tracks. Track offset information is presently not printed in the BWF header chunk.

What kind of record buffering, or pre-roll is available?

The user can select to engage pre-roll buffers of up to 10 seconds (sample rate/bit depth dependent). This means that the recorded file will begin at the moment in time when the record button is pressed minus the number of pre-roll seconds set in the unit. Pre-roll is useful to add additional head information on the file or to capture audio that may have been missed by not engaging record. Pre-roll is becoming a standard feature on the new file-based video cameras, as well.

Are tracks assigned to their own files or as stereo pairs (or some other way)?

Audio files can be written as either multiple mono files or as polyphonic files. This is selectable in the user menu. How many tracks that are recorded is determined by the input routing matrix. If any input is assigned to any recording track, then that track is active and audio information is recorded.

Workstation software varies in its support for mono and polyphonic .wav and .bwf files. Consult you software vendor or post-production coordinator regarding supported formats.

I know that all audio signals are digitized as soon as they are input to the recorder. Also, headphone monitoring and analog outputs are always fed from the digital-to-analog converter. What is the delay (latency) from analog input to analog output?

The latency from input to output on the recorders is sample rate dependent. Whether 16 or 24 bit, these numbers are identical.

• @ 48 kHz – 1.47 ms
• @ 96 kHz – 0.75 ms
• @ 192 kHz – 0.23 m

General:

How long does the unit take to power up and be ready to record?From a cold start to recording to either hard drive or CF medium the 7-Series recorders take approximately four seconds. You can cancel the cute Sound Devices logo splash screen by pressing the stop key during power up.
What is the function of the C. Link ports?

The C. Link (control link) port interconnects two or more 7-Series recorders and locks their word clock. on the 744T the C. Link also carried time code output. C. Link is also “big brother”, with the ability to retrieve all kinds of data stored in the unit’s EEPROM. It is our primary test/diagnostic input. In the future, we will allow third-party access to features available on the C. Link port.

The new CL-1 accessory provides for keyboard control and remote roll via C. Link. More information on the CL-1 is available here.

Can the front panel controls be locked out to prevent unintended adjustment?

Yes, all front panel controls can be locked out by holding the brightness button and tone oscillator button simultaneously. In addition, when recording is occurring no button, including power, will take the unit out of record, except for a 200 ms hold of the stop/pause button. Recording is the primary function and the interface is designed to safeguard recording activity.
Can the FireWire output be used to plug in a computer and use the recorder as a “sound card”, ie. for recording without latency on a software multitrack?

FireWire is presently for file transfer only. There is presently no provision for isochronous data transfer via FireWire. You could, however, use the AES3id output and connect to a computer’s S/PDIF coaxial input for realtime digital audio transfers.

This entry was created on Monday, November 19, 2007 and is filed under Digital Recorders. Article 118